Heavy Metals

Heavy Metals

Cadmium and some other heavy metals are natural constituents of seawater but can also be considered as conservative pollutants. Increased concentrations of these metals may be present in marine organisms due to bioaccumulation. Therefore, marine contamination by even low concentrations of heavy metals can disturb marine ecosystems (Radenac et al. 2001). The toxic as well as the potential mutagenic and teratogenic effects caused by cadmium have been described in many organisms (Flick et al. 1971), including marine invertebrates (Schr der et al. 1999b). They involve the production of ROS, DNA strand breaks, and inhibition of DNA synthesis and repair enzymes (Hartwig 1994 Schr der et al. 1999b) Studies on ROS production in response to environmental factors and contaminants, such as heavy metals and polychlori-nated biphenyls (PCBs),by echinoderm immune effector cells are reviewed by Coteur et al. (this Vol.). In particular, marine sponges are able to accumulate high amounts of cadmium (M...

Defining the terms and scope of food and nutritional toxicology

In essence, toxicology is the science of poisons, toxicants, or toxins. A poison, toxicant, or toxin is a substance capable of causing harm when administered to an organism. Harm can be defined as seriously injuring or, ultimately, causing the death of an organism. This is a rather simplistic definition, because virtually every known chemical or substance has the potential for causing harm. The term toxicant can be a synonym for poison, or the term poison might be more appropriate for the most potent substances, i.e., substances that induce adverse effects at exposure levels of a few milligrams per kilogram of body weight (see later discussion). The term toxin usually refers to a poison derived from a protein or conjugated protein produced by some higher plant, animal, or pathogenic bacteria that is highly poisonous for other living organisms, e.g., botulinum toxins. Toxicologists study the noxious or adverse effects of substances on living organisms or on in vitro surrogate models,...

General Physiology of Nutrient Absorption

Nutrients enter the blood by passing through the intestinal mucosa. Intestinal nutrient transport can occur via two distinct pathways. One is termed the paracellular pathway and represents the movement of a nutrient between the absorptive enterocytes on the intestinal villi. This transport pathway is an energy-independent diffusional process and depends on the electrochemical gradient across the mucosa and its permeability characteristics to the nutrient in question. The characteristics of the diffusional pathway are not regulated in response to nutrient deficiency or excess. A second transport pathway represents the transcellular movement of a nutrient across the intestine. The transcellular transport rate of the nutrient is composed of both diffusional and carrier-mediated transport pathways. Often in response to changes in nutrient status the number of nutrient carriers will be changed to facilitate appropriate increases or decreases in intestinal absorption to help maintain...

Membranous Glomerulopathy

Membranous Glomerulopathy

Membranous glomerulopathy is a major cause of the nephrotic syndrome in adults (1,2). Only in the past decades has it been surpassed by focal and segmental glomerulosclerosis as the main cause of the nephrotic syndrome (3-5). Membranous glomerulopathy develops mostly idiopathically, but can also be seen in relation with and possibly secondary to, among others, hepatitis B, Sjogren's syndrome, transplantation, lupus erythematosus, diabetes mellitus, sarcoidosis, syphilis, exposure to certain drugs and heavy metals (penicillamine, bucillamine, gold, mercuric chloride), and malignancies (10 ), including carcinomas, carcinoids, sarcomas, lymphoma's, and leukemias (2,6-10). The possibility of a malignancy must be considered especially in older patients with membranous glomerulopathy. In these patients it is also imperative to perform urinary immunoelectropho-resis routinely to rule out myeloma and renal primary amyloidosis (AL) (2). Finally, idiopathic membranous glomerulopathy, of which...

Xenobiotics and Other Problematic Chemicals

The word is derived from the Greek 'xenos' meaning foreign. Throughout this book the definition used is that xenobiotics are compounds which are not produced by a biological procedure and for which no equivalent exists in nature. They present a particular hazard if they are subject to bioaccumulation especially so if they are fat soluble since that enables them to be stored in the body fat of organisms providing an obvious route into the food chain. Despite the fact that these chemicals are man made, they may still be degraded by micro-organisms if they fit into one of the following regimes gratuitous degradation, a process whereby the xenobiot resembles a natural compound sufficiently closely that it is recognised by the organism's enzymes and may be used as a food source, or cometabolism where the xenobiot is degraded again by virtue of being recognised by the organism's enzymes but in this case its catabolism does not provide energy and so cannot be the sole carbon source....

Heavy metal pollution

Pollution with heavy metals (particularly zinc, copper, and lead) often accompanies conditions of high acidity and typically arises as a result of industrial contamination or acid mine discharge. Lake D'Orta (Italy) provides a good example of industrial pollution, with a history of initial copper contamination ( 1930-1960), followed by mixed pollution with Cu, Zn, Ni, and Cr plus acidification. The microbial response to these extreme conditions was investigated over the time period from sediment cores (Cattaneo et al., 1998) in relation to two main groups - diatoms (algae) and thecamoebians (protozoa). In both cases, the stress response involved a decrease in individual mean size, which reflected a shift in the taxonomic composition of the microbial assemblages. Within the diatoms, communities dominated by Cyclotella comensis (biovolume 100-1000 mm3) and Cyclotella bodanina (100010 000 mm3) were replaced by assemblages dominated by Achnanthes minutissima (

Button Battery Ingestion

A button battery lodged in the esophagus is a true emergency because of the extremely rapid action of the alkaline substance on the mucosa. Burns to the esophagus have been reported to occur in as little as 4 h, with perforation as soon as 6 h after ingestion. Button batteries in the esophagus require emergency removal if significant morbidity is to be averted. Outcome does not appear to be affected by battery discharge state but is affected by chemical composition. 12 Lithium cells are associated disproportionately with adverse outcome. Mercuric oxide cells tend to fragment more frequently than other cells however, the threat of heavy metal poisoning has not been supported by the literature or clinical experience. This fact notwithstanding, blood and urine mercury levels should be measured whenever a mercury-containing cell is observed to have split while in the gastrointestinal tract.

The North Sea A Norwegian Fiord as a Natural Gradient of Metal Contamination

An interesting confirmation of the results obtained in field studies came from the analysis of hsp70 levels present in coelomocytes from the sea star Asteria rubens collected in the Norwegian fiords during the campaign held in May-June 2000, thanks to collaboration with Drs. Coteur and Dubois. The fiord, located in southwestern Norway, is about 38 km long, 1-3 km wide, and at maximum 390 m deep (see for details Coteur et al. 2003). The study area and sampling sites are extremely interesting because they constitute a sort of natural dose-dependent open-sea laboratory where the heavy metal concentration decreases going from the head of the S0rfjord, where first zinc then titanium iron smelters are located, to the open sea. In fact, studies on the accumulation of Cd, Pb, Zn, and Cu in the sea star Asteria rubens, living along the natural gradient, demonstrated a direct relationship with the level of contamination of the environment, at least for Cd and Pb (Coteur et al. 2003). We then...

Principles of immunoelectron microscopy

In preparation for transmission electron microscopy, samples are usually fixed with aldehydes (glutaraldehyde, formaldehyde or a combination of the two), post-aldehyde fixed in osmic acid, en bloc stained with a uranyl acetate solution, dehydrated with alcohols and embedded in a plastic resin. The embedded samples are thin sectioned with a glass or diamond knife and subsequently counterstained with heavy metals (uranium and lead salts) to further enhance the electron density of positively or negatively charged molecules in the sample. Specimens thus prepared have good contrast and can be used to observe and record the molecular and subcellular detail of cells and tissues. Alternatively, molecules may be adsorbed to a thin plastic film followed by embedding in an electron-dense stain or angular shadowing with evaporated metals.

Essential Features of Biological Treatment Systems

In the final analysis, all biological approaches are expressly designed to optimise the activities of the various micro-organisms (either native to the particular soil or artificially introduced) to bring about the desired remediation. This generally means letting them do what they would naturally do but enhancing their performance to achieve it more rapidly and or more efficiently. Effectively it is little different from accelerated natural attenuation and typically involves management of aeration, nutrients and soil moisture, by means of their addition, manipulation or monitoring, dependent on circumstance. However simple this appears, the practical implications should not be underestimated and careful understanding of many interrelated factors is essential to achieve this goal. For example, successful aerobic biodegradation requires an oxygen level of at least 2 mg litre by contrast, when the major bioremediation mechanism is anaerobic, the presence of any oxygen can be toxic. The...

Aerobes and Effluents

Moreover, the extension of sewage treatment facilities to ameliorate trade effluents also has implications for the management of true sewage sludge. It is not economically viable to develop processing regimes which do not lead to the concentration of toxic contaminants within the derived sludge. This was shown to be a particular problem for plants using the activated sludge process, which relies on a high aeration rate for pollutant removal, which proceeds by making use of biotransformation, air stripping and adsorption onto the biomass. Adsorption of toxic inorganic substances like heavy metals, or structurally complex organic ones, onto the resident biomass, poses a problem when the microbial excess is removed from the bioreactor, particularly since dewatering activities applied to the extracted sludge can, in addition, catalyse a variety of chemical transformations. Accordingly, sewage sludge disposal will always require careful consideration if the significant levels of these...

Adaptive Gene Amplification

Gene amplification has been identified as a fundamental evolutionary response in bacterial populations exposed to various selective pressures (108, 110,123) and has been implicated, for instance, in adaptation to heavy-metal toxicity (62) and to growth on limiting carbon sources (122,134). The principal benefit of gene amplification is that it is freely reversible by homologous

Determinants of Toxicity

The toxic potential of hydrocarbons depends on physical characteristics (volatility, viscosity, and surface tension), chemical characteristics (aliphatic, aromatic, or halogenated), presence of toxic additives such as pesticides or heavy metals, route of exposure, concentration, and dose. Viscosity, defined as the resistance to flow, and surface tension, denoting creeping ability, both play a major role in determining the aspiration potential. Viscosity is measured in Saybolt Seconds Universal (SSU). Patients ingesting substances with viscosities less than 60 SSU (e.g., gasoline, kerosene, mineral seal oil, turpentine, and aromatic and halogenated hydrocarbons) are at greater risk for aspiration than those ingesting substances with viscosities greater than 100 SSU (e.g., diesel oil, grease, mineral oil, paraffin wax, and petroleum jelly). Low surface tension also increases the risk of aspiration. Volatility denotes the ability of a substance to vaporize. Inhalation of highly volatile...

TABLE 1745 ED Management of Hydrocarbon Exposures

The patient needs to be fully undressed to prevent ongoing contamination from hydrocarbon-soaked clothes. Dermal decontamination with soap and water, and eye decontamination with saline irrigation, should be performed. Pre-hospital decontamination is preferable. The staff should wear protective gloves and aprons to prevent possible secondary exposure. Specific antidotal treatment directed at the complications of toxic additives, such as organophosphates or heavy metals, may also be needed.

Introduction Clinical Setting

Broadly speaking, ATN may be the result of one of two mechanisms ischemia or toxin induced. The structural changes in each are reasonably distinctive, and pathogenic mechanisms are also considered different. Traditionally, ischemic ATN follows hypotension or hypovolemia or both (3,4). There may be many causes of this circulatory state these include extensive trauma with rhabdomyolysis and myoglobinuria, incompatible blood transfusions, pancreatitis, septic shock in a variety of settings, extensive hemolysis as in malaria (blackwater fever), and shock following administration of barbiturates, morphine, and sedatives. Toxic ATN is a dose-dependent injury with extensive tubular cell necrosis normally limited to a specific portion of the nephron and usually involving almost all neph-rons. This is obviously in sharp contrast to ischemic tubular necrosis in which the changes are considerably more subtle and patchy. Many therapeutic and diagnostic agents, industrial chemicals, heavy metals,...

Effects of Polluted Sediment on Plankton Dynamics

The previous experiments showed the effects of selected pesticides and metals on zooplankton grazing. Similar effects were observed in the semi-natural situation of natural sediment, from a polluted and a relatively pristine location, which was left for several years in outdoor mesocosms (2 m3, 30 cm sediment layer) (Foekema et al. 1998). The polluted (Lake Ketelmeer) and unpolluted (Lake Oostvaardersplas-sen) sediments were very similar with regard to their physical and chemical (e.g. nutrient) characteristics, but differed in their content of pollutants (esp. several heavy metals and PAHs).

Genetic Engineering Of Microorganisms Used For The Production Of Citric Acid

Metabolic flux through the pathway leading to citric acid formation. (4) There is a direct increase of the flux through the main pathway (i.e., by overproduction of the enzymes involved in the production of the acid). (5) Finally, they tolerate high concentrations of heavy metals and produce large amounts of citric acid when they are grown in molasses solution (3).

Study questions and exercises

Heavy metals interact extensively with sulfur amino acids, and dietary selenium has been known to follow the sulfur pathway. Suggest a mechanism of action for selenium's purported usefulness in protecting against heavy metal toxicity. Search the literature for reports on the interaction of selenium and heavy metals. 4. Heavy metal toxicity seems to be aggravated by reduced antioxidant status. What mechanism may be responsible for this aggravation

Definitions and classification of agglutination reactions

To antigenic components adsorbed or chemically coupled to red cells or inert particles (passive hemagglutination and passive agglutination, respectively). Erythrocytes are also agglutinated by nonantibody substances such as plant proteins, viruses, salts of heavy metals, inorganic colloidal acids and bases, and basic proteins (protamines, histones). Agglutination inhibition or hemagglutination inhibition refers to the inhibition of these reactions by soluble antigen which reacts with the combining sites of the antibodies and thereby prevents their binding to and agglutination of the particles.

Limitations And Potential

The option of last resort is to treat and dispose of the waste in safe landfills, while minimizing the resultant volume, since disposal sites are few and space is precious not to mention expensive. A given bioremediation technology should be able to perform on a large scale in order for it to be commercially viable. The organism or biomaterial selected to accomplish the goal of removing or altering a heavy metal or metal ion rendering it less toxic must be very efficient in performing its intended function. The literature is rich with reports of studies attesting to the potential of a particular biomass or biomaterial to carry out bioremediation of metal-contaminated waste streams, but few have actually ventured beyond the laboratory bench scale. What is clear is the apparent dearth of genetic engineering reports in the literature. Classical genetic selection methods have proven useful, for e.g., for isolating a strain of S. cerevisiae out of 240 tested, capable of uptake of 3.2 mg...

Transient Conditions And Stresses In Engineered Biological Treatment Systems

Toxicity in anaerobic systems is generally related to the inhibition of methanogens by the increase in concentration of VFA, particularly, butyrate and acetate, but it can also be associated with sulfide and heavy metals, as reviewed in refs 56 and 57. The inhibitory effect of VFA is related to the lowering of pH. Since substrate concentration and temperature transients can lead to the accumulation of VFA, the effect of these transients can be compounded by a pH inhibitory effect on methanogens.

Extracellular Precipitation of Metals

Exceeding a solubility product leads to precipitation of an insoluble salt of the reacting species. Sulfide anion (S22) and oxalate anion (C2O4_) are produced by some species of micro-organisms and these anions can form very insoluble salts with heavy metal ions which exhibit very small solubility products as noted by Veglio and Beolchini (1997). Copper phosphate precipitation occurring within the matrix of mycelia of the fungus Penicillium ochro-chloron after 4 days of incubation in shake flask cultures at pH 4, was demonstrated using scanning electron microscopy and energy dispersive x-ray microanalysis (Crusberg et al. 1994). Wrinkled 40-50 mm dia. spheres of insoluble copper phosphate, inferred from EDX analysis, are trapped within the mycelia of the fungus grown for 4 days in aerated cultures in the presence of 100mg l Cu2+. Penicilllium and Aspergillus have been shown to produce extracellular acid phosphatases which correlate with copper removal from solution (Haas et al. 1991...

Tertiary Structure and Protein Domains

The local foldings, evident in secondary structure, then combine into a single polypeptide chain. This chain is called the tertiary structure, or conformation. For example, the pancreatic enzyme ribonuclease, which aids in digestion of RNA in the diet, consists mainly of beta sheet folds, with three small alpha-helical regions. Tertiary structure is often stabilized by disulfide bonds between adjacent cysteine in different regions of the protein. For example, the tertiary structure of ribonuclease contains four disulfide bonds, located at specific sites. The stability of the tertiary structure of proteins is destroyed by toxic heavy metals such as mercury. Concentrations of mercury in the environment, for example, result in the displacement of hydrogen on the sulfur atom (SH), thereby blocking functional disulfide bonds.

Special Groundwater Wells

Additional elements can include nutrient infiltration pipes within the well. An electric water pump may be installed instead of the mammoth pump. If so, no stripping and no oxygen enrichment of the groundwater occur. An electric pump may also be installed in addition to a mammoth pump. Furthermore, a permeable bioreac-tor containing immobilized contaminant-degrading bacteria can be installed between the points of water input and output. However, the water flow velocity is usually too high to allow significant degradation of the contaminants within the residence time in the bioreactor. Therefore, the reactor material also contains activated carbon. The contaminants are sorbed onto the carbon, which is reactivated by biodegradation of the contaminants within the reactor. The reactor may also contain other materials such as an ion exchanger (to remove heavy metals) or only activated carbon, if the contaminants are not sufficiently biodegradable (e.g., PAH).

Evolving Technologies

Most of the evolving technologies have been investigated only on the laboratory scale, but some have already been tested on a pilot or even technical scale. However, detailed experience and wide commercial use are not available. Until now heavy metals have been treated with physicochemical technologies. Although these elements are not 'degradable', they are not biochemically inert. Several microbiological transformations are known that mainly alter the physicochemical behavior of metals 12 , including cause the efficiency of phytoremediation is restricted to the depth of root growth. Some contaminants, e.g., nitroaromatics, are taken up but are not transported within the plant. Transformation of the contaminants is usually not effective enough for final elimination and is therefore of minor importance. For example, heavy metals can be accumulated without significant transformation by some plants to a very high extent. Hence, for final removal of the contaminants, the plants have to be...

Criteria For Evaluation

Technical evaluation of swine waste management systems considered ''environmentally superior'' includes consideration of the following performance parameters 1) prevention of waste discharge to surface or ground water 2) elimination of emissions of ammonia and odors to the atmosphere 3) elimination of discharge of pathogens and disease vectors 4) elimination of discharge of nutrients and minerals, especially heavy metals, to soil 5) operational and economic feasibility and 6) acceptability for permitting by local authorities. A detailed discussion of a program that addresses all of these parameters under full-scale performance testing conditions is found in Ref. 5.

Food Biotechnology References

Effect of potassium ferrocyanide on the chemical composition of molasses mash used in the citric acid fermentation. Biotechnol. Bioeng. 7 269-278, 1965. Clark, D.S., K. Ito, H. Horitsu. Effect of manganese and other heavy metals on submerged citric acid fermentation of molasses. Biotechnol. Bioeng. 8 465-471, 1966. Banik, A.K. Mineral nutrition of Aspergillus niger for citric acid production. Folia Mikrobiol. 21 139-143, 1976.

Therapeutic Implications

Tions and through affecting the redox status of thiol-containing proteins (9). Indeed, a-lipoic acid can be thought of as a metabolic antioxidant since it is a naturally occurring substance reduced by several cellular enzymatic systems. Beneficial effects of lipoic acid administration have been reported in diabetic complications (22,23), having been used in the treatment of diabetic neuropathy in Germany ischemia-reperfusion injury (24) and liver disease (23). Furthermore, lipoic acid is be a good candidate for treatment in AIDS, neurodegenerative diseases (21), or heavy metal poisoning (9).

Whole Bowel Irrigation

Contraindications include patients with preceding diarrhea, ingestions that are expected to result in significant diarrhea (except for heavy metals, as these substances do not adsorb well to activated charcoal) and patients with absent bowel sounds or with obstruction. The complications included bloating, cramping, and rectal irritation from frequent bowel movements. Close nursing care is needed to maintain patient cleanliness.

Bile Secretion And Gall Bladder Function

Bile Acids

Micellar formation is essential for the optimal absorption of fat digestion products. Bile also serves as a vehicle for the elimination of a variety of substances from the body. These include endogenous products like cholesterol and bile pigments, as well as some drugs and heavy metals.

The Algae Cyanobacteria

Phosphorus into biomass, thereby reducing the eutrophication potential of receiving waters. The immobilized cyanobacteria can also remove heavy metals, nutrients, and toxic organic compounds due to their affinity for these contaminants (13). Cyanobacteria serve as a food source in various parts of the world in the past, the main focus has been on the production of single cell protein (SCP), although other applications that require mass cultivation are apparent. For instance, the cyanobacterium Spirulina platensis is grown commercially and the biomass is used as a health food worldwide. It is also reported that cyanobacteria are a rich source of type II restriction endonucleases, some of which are currently marketed. Other products from cyanobacteria include amino acids and pigments that can be used as food colorants and diagnostic probes (13). It is worth noting that some hydrophilic pigments have been marketed. Phycobiliproteins, especially phycoerythrin, are stable pigments that can...

Water And Wastewater Disinfection Treatment

Wastewater Disinfection

A wide range of nonoxidizing organic and inorganic chemicals are used for, or are able to provide, disinfecting effects, including aldehydes (formaldehyde and glutaraldehyde), phenolics, alchohols (ethanol and isoproponal), cationic detergents, nitrites, and heavy metals (e.g., mercury, silver nitrate, tin, arsenic, copper). Although most of these chemicals have little relevance for the disinfection of waters, wastewaters, or sludges, there are two noteworthy exceptions. Specifically, silver-impregnated filters are sometimes marketed for point-of-use water conditioning devices, such as those that are sometimes screwed onto the outlets of sink faucets. In this instance, the silver is intended to be slowly leached from the filter medium (typically, activated carbon) at a rate that, hopefully, will retard the opportunistic formation of microbial biofilms intent on using sorbed organics as their energy source. A second nonoxidizing chemical disinfectant option is that of using cationic...

Validation Studies of Dynamic Contrast Enhanced MRI

Oesophage Marteau Piqueur

The DCE-MRI approach is widely used to draw inferences into microvascular parameters such as microvascular permeability, blood volume, and tissue perfusion. Confirmed insight into the whereabouts, and amount of the tracer, at the tissue level would unquestionably help to determine the most accurate and precise way to model the signal changes in DCE-MRI. This can be accomplished by correlating DCE-MRI with quantitative transmission electron microscopy (TEM) methods. TEM can be used, in combination with energy dispersive X-ray spectrometry (EDXS) microanalysis to assess the subcellular content and location of heavy metals like gadolinium and iron (Elster 1989 LoPachin and SaubermanN 1990 Taherzadeh et al. 1998). This method analyses the characteristic X-ray patterns, produced from the heavy metal based MRI contrast agents when an electron beam passes through the tissue. Where the concentration is high enough elemental distribution maps can be produced (LoPachin and Saubermann 1990). A...

Heavy Metal Intoxication

Ingestions of one of several heavy metals can lead to systemic manifestations. Lead poisoning, or plumbism, is the most common heavy metal poisoning. Systemic signs of lead poisoning are highly variable depending on the age of the patient and the amount of lead ingested. Symptoms range from colic, iritability, fatigue, and anemia to encephalopathy. Intraorally, lead poisoning presents as an ulcerative stomatitis or a bluish hue to the buccal mucosa. The classic bluish lead line on the ginigiva, secondary to subepithelial deposits of lead sulfide, also may be seen. In addition, a tremor on tongue thrusting, excessive saliva production, metallic taste, and severe periodontal disease may occur. Treatment is chelation therapy.40

Environmental Contaminants

Of deposition of environmental lead into the plants. The elimination of leaded gasoline, lead in soldered food cans, and lead in pottery glazes have all contributed to a decrease in the levels of lead in food. Fish, plants, and animals take up cadmium from the environment, and shellfish are the major source of cadmium in the diet. Mercury exposure via food most often occurs when fish and seafood are contaminated with mercury. The Food and Drug Administration (FDA) limits the amount of heavy metals in our foods. For example, cadmium in food colors is limited to 15 parts of cadmium per million parts of food color (15 ppm), and the maximum acceptable level of mercury in fish and seafood is set at 0.5 ppm.

Naturally Occurring Toxicants

Tablished for various nutrients and pharmaceuticals. The phenomenon is called hormesis and is defined as the production of beneficial effects in a population at low exposures and adverse effects at high exposures to a given chemical. Data demonstrating that hormesis may occur with compounds that have previously been considered only as toxins, such as pesticides and heavy metals, has recently been reviewed (13). It appears likely that this holds true for many plant compounds as well. For example, tannins represent a group of natural plant compounds that have been shown to have both beneficial and toxic effects (15).

Chemical Toxins And Radiation

If you or your partner might be exposed to a potentially harmful substance, take steps to avoid it. Think about your home and workplace. Jobs involving heavy metals such as lead or mercury, chemicals in pesticides, or chemicals used in certain manufacturing (such as painting or printing) processes may be harmful to your fertility. Some of these toxins have been shown to damage sperm. These environmental toxins may also cause problems with the development of your unborn baby's central nervous system.

Introduction the law and food intolerance

Throughout history laws have existed to protect the consumer against the adulteration of food, whether deliberate or accidental. Watering down of milk and the contamination of food with heavy metals have long been the subject of investigation and prosecution. How does this translate into modern life and the problems of food intolerance The first point to be clear about is that with a few minor exceptions, the law does not specifically recognise or refer to the problem of food intolerance and allergic reactions. It is therefore necessary to examine the legal provisions that do exist in order to see where they can be of help to the sufferer and provide protection against inadvertent consumption of a food which may give rise to a reaction.

Genetic control of leaf senescence and fruit ripening

Phloem during senescence and are regarded as the main transportable amino acids (Buchanan-Wollaston and Ainsworth, 1997). ATP sulphurylase is involved in the biosynthesis of cysteine and methionine. It has been proposed that during senescence the up-regulation of ATP sulphurylase leads to a subsequent increase in the cysteine pool. Cysteine is the precursor for glutathione biosynthesis, a major antioxidant, which, in addition to its role in the recovery of ascorbate and scavenging of reactive oxygen species (ROS), also acts in the transport and storage of sulphur (Rennenberg, 1982), the regulation of cell division and development (Earnshaw and Johnson, 1985), the regulation of gene expression and signalling (Wingate et al., 1988 Herouart et al., 1993 Moran et al., 2001) and the detoxification of xenobiotics and heavy metals (Delhaize et al., 1989 Halliwell and Gutteridge, 1986 Timmerman, 1989).

Practical Toxicity Issues

Although we have been considering the issue of metal toxicity in relation to the contamination of land or water, it also has relevance elsewhere and may be of particular importance in other applications of biotechnologies to environmental problems. For example, anaerobic digestion is a engineered microbial process commonly employed in the water industry for sewage treatment and gaining acceptance as a method of biowaste management. The effects of metal cations within anaerobic bioreactors are summarised in Table 4.2, and from which it is apparent that concentration is the key factor.

Experimental Approach

Metallothioneins are possibly involved in detoxification processes in marine organisms occurring after exposure to heavy metals such as cadmium, zinc and copper (Bonham et al. 1987 Lyons-Alcantara et al. 1998 Cajaraville et al. 2000). Therefore, we also investigated the effects of exposure to sublethal concentrations of cadmium chloride on the expression of the metallothionein gene during the development of P. lividus sea urchin embryos (Russo et al. 2003). Northern blot analysis and RT-PCR experiments revealed that the metallothionein gene is constitutively expressed at low levels in control embryos at cleavage, swimming blastula, late gastrula and pluteus stages (6,12,24 and 48 h after fertilization Russo et al. 2003). The levels of metalloth-ionein transcripts increase with the developmental stage, in agreement with results reported by others (Wilkinson and Nemer 1987). However, when embryos were cultured in the presence of sublethal concentrations of cadmium chloride and harvested...

Neurotoxic Contaminants

These insecticides are strongly suspected to be harmful, and clearly they are in the case of acute intoxication, when organisms come into contact with high doses, generally as a result of accidents or occupational exposure. However, there is also the possibility of subtle chronic (low-dose, long-term) damage due to aerosol diffusion, or to residuals in crops and vegetables, possibly reinforced by the presence of traces of other pollutants, such as other neurotoxic substances, heavy metals and hydrocarbons, among others. On the other hand, the no-effective concentration for humans (NOEC), indicated by the pharmaceutical companies and databases, is not surely ascertained, because it is obtained by experimental exposure of animals, generally rats or mice, and then by estimating it as several-fold lower. Moreover, the doses that do not

TABLE 1998 Commonly Treated Forms of Internal Contamination

Chelating agents such as calcium and zinc salts of diethylenetriamine pentaacetic acid (Ca-DTPA and Zn-DTPA, respectively) are effective treatments for contamination with heavy metals and rare earths that emit alpha radiation. If alpha-emitting contamination is detected in wounds or in the nares or oropharynx, treatment with DTPA should be initiated promptly, ideally within 1 to 2 h after contamination has occurred. Potential contraindications for the use of DTPA are severe renal dysfunction, thrombocytopenia, or leukopenia. DTPA is administered systemically by slow IV push or by aerosol administration. Ca-DTPA has been shown to be more effective in animal studies and is the preferred form of drug for the initial one to two days of treatment. Zn-DTPA is less toxic and recommended for treatments of longer duration and of pregnant females. For aerosol administration, Ca-DTPA is preferred because of the metallic taste associated with Zn-DTPA. Most DTPA solutions in nuclear medicine...

Detection And Purification Of Biochemical Compounds

Immunoassay uses antibodies to form a precipitate with specific compounds. Antibodies are special proteins produced by the body to bind with foreign substances so that they can be made harmless. Each antibody is highly specific, binding only to a single substance and binding extremely tightly in what is called a lock-and-key relationship. Molecular biology techniques have enabled the production of large quantities of antibodies of a specific type, called monoclonal antibodies. They are used for research purposes as well as to detect specific hormones in pregnancy tests and tests for prostate cancer. Immunoassay is a highly sensitive and selective detection method. Its use has been extended to organic pollutants and even to heavy metals.

Good agricultural practice

Though GMP has been developed for the food manufacturing industry, the principles on which it is based are readily transferable to the growing of fruit and vegetables. In this instance the appropriate term is good agricultural practice or GAP. Growers undertake many activities that have the potential to generate hazards that may be associated with produce given the right circumstances, but which might not be included as requirements for control within the scope of HACCP systems. General site organization and cleanliness will lead to the minimization of sources of contamination that might compromise food safety. The handling, storage and methods of use of agrochemicals ought to be carried out in defined ways that are unlikely to lead to the creation of food safety hazards. Equipment used to apply agrochemicals, for example crop sprayers, should be calibrated to ensure correct levels of chemical application and should be cleaned between uses to prevent the possibility of...

Natural Plant Bioremediators

For many millions of years, plants have adapted to the presence of various metals in varying amounts in soils. Some metals, such as zinc, nickel, cobalt, and copper, function as nutrients when eaten by humans in small amounts, but are toxic when consumed in excess. Heavy metals that are toxic even in trace amounts include mercury, lead, cadmium, silver, gold and chromium. Human activities such as mining, municipal waste disposal, and manufacturing have increased heavy metal pollution to dangerous levels in some areas. These chemicals cause oxidative damage, which destroys lipids, DNA, and proteins. Certain plants, called hyperaccumulators, cope with excess heavy metals in the environment by taking them in and sequestering them in vacuoles, which are bubble-like structures in their cells. Sometimes the plant combines a pollutant with another molecule, a process called chelation. Organic acids often serve this role. Citric acid, for example, surrounds and thereby detoxifies cadmium, and...

Mycorrhizae And Bioremediation

In the mining process, not only plants are removed, but also upon soil replacement changes in texture and deposits of salts and heavy metals often result (Allen 1989). The toxicity of The mechanism that confers heavy metal tolerance in mycorrhizal fungi is largely unknown. The survival of AM and EM fungi in polluted soil may depend heavily on the density of the external hyphae. The absorption of heavy metals to the hyphal surface could reduce soil concentrations and thus accumulation of fungal and plant tissue (Denny and Wilkins 1987 Marschner and Dell 1994). Components of the fungal cell wall, such as chitin and melanin, can bind heavy metals to the extraradical mycelium (Denny and Wilkins 1987 Tam 1995). Turnau et al. (1996) found that the EM fungal mantle contained the highest levels of heavy metals while the Hartig net contained the lowest levels. Glomalin, the glycoprotein that coats AM fungal hyphae, could play an equally important role in protecting AM fungi and host plants...

Solid Waste Treatment

Extending beyond water presence, a number of additional ambient environmental conditions come into play. Nutrient availability will certainly be an issue, not only in regard to the macroscale distribution of carbon and nitrogen (i.e., for which a C N ratio of 20 1 is typically considered optimal), but also in terms of the available presence of lower-level essential elements (e.g., phosphorus, sulfur, potassium, iron, calcium). While the pH of the constitutive moisture must also be suitably conducive to microbial activity, fermentative metabolism will progressively release weak organic acids that could well shift the pH to a more acidic, and less optimal, state. In fact, a downward shift in pH of this sort might accordingly escalate the undesired rate of trace metals leaching from the waste matrix, thereby leading to inhibitory metal toxicity.


Several factors affect the stability and resulting anti-mycotic activity of natamycin. While pH has no apparent effect on antifungal activity, it does influence stability of the compound. In the pH range of most food products (pH 5-7), natamycin is very stable. Under normal storage conditions, temperature has little effect on natamycin activity when in neutral aqueous suspension. Sunlight, contact with certain oxidants (eg, organic peroxides and sulfhydryl groups), and heavy metals all adversely effect stability of natamycin solutions or suspensions (67).


Singlet oxygen is short-lived and reverts back to the ground state with the emission of light. This light is fluorescent, meaning its wavelength is higher than that of the light originally absorbed. The reactivity of single oxygen is 1500 times greater than that of normal oxygen. Compounds that can act as sensitizers are widely occurring food components, including chlorophyll, myoglobin, ribo-flavin, and heavy metals. These sensitizers are activated by light and then produce singlet oxygen. The singlet oxygen reacts directly with the double bond by addition and causes the double bond to shift away by one carbon atom. Singlet oxygen attack on linoleate produces four hydroperoxides. Photooxidation has no induction period, but the reaction can be stopped by compounds known as quenchers. These quenchers compete for the singlet oxygen and return it to the ground state. Carotenoids are widely occurring quenchers. Rahmani and Saari Csallany (1998) reported that in the photooxidation of...


The growth and metabolic activity of bacteria within the surface biofilm is influenced by opposing environmental factors. These aspects are promoted by high nutrient levels, but may be limited by unstable temperature conditions, localized accumulation of organic toxins and heavy metals, and intense levels of UV and visible solar radiation. In spite of this environmental stress, studies on nutrient


Supercritical extracts therefore have a unique and concentrated spectrum of lipophilic ingredients. They have the general advantage of being free of solvents, inorganic salts and heavy metals. They are practically sterile 10 and they need no preservatives since they do not provide a base for germ growth due to the absence of water, proteins and polysaccharides. All this allows a safe application and simple declaration. - no inorganic salts or heavy metals

The Small Intestine

Some of the interactions between cell wall poly-saccharides and other food components in the small intestine are much more specific. There has been considerable interest over a number of years in the possibility that the polysaccharides and complex phenolic components of cell walls contain polar groups that could interact with and bind ionized species in the gastrointestinal contents, thereby reducing their availability for absorption. Intraluminal binding of heavy metals, toxins, and carcinogens might be a valuable protective mechanism, but binding of micronutrients could seriously compromise nutritional status.


A, B, and C Radiographs of the knee and ankle show the bone-in-bone phenomenon, which can result from heavy metal poisoning or serious illness during bone growth. One can see the faint outline of the smaller bone at the time of the insult encased in the larger mature bone. This individual had ingested phosphorus during bone growth because of a habit of chewing matches. We have seen similar changes following severe childhood typhoid fever. A somewhat similar appearance can be seen in osteopetrosis or treated histiocytosis X.

Fish Minerals

See also Cancer Epidemiology and Associations Between Diet and Cancer. Coronary Heart Disease Prevention. Dietary Guidelines, International Perspectives. Fatty Acids Omega-3 Polyunsaturated. Food Composition Data. Food Safety Bacterial Contamination Other Contaminants Heavy Metals. Hyperlipidemia Nutritional Management. Iodine Physiology, Dietary Sources and Requirements. Protein Quality and Sources. Stroke, Nutritional Management. Supplementation Dietary Supplements.

Sea Urchins

Although DNA repair enzymes (e.g. photolyases) protect sea urchins, UV radiation may cause direct damage to DNA by formation of pyrimidine dimers or cross-links between DNA and protein. As a consequence, delayed cell divisions, developmental delays, and abnormalities may occur. In a European Union project ( UVTOX ), sea urchin coelomocytes have recently been used as a novel biosensor of the effects caused by UV-B and heavy metals (cadmium) and their combinations (Schr der et al. 2000a).

Particulate Markers

A variety of heavy metals and rare earth elements, particularly those forming strong bonds with feed digesta particles, have been successfully employed as particulate markers. An important prerequisite is that these elements are either not present or present in minimal concentration in soil and plants. Metal oxides (Cr and titanium) have been proposed as digestibility markers. Chromium sesquioxide (Cr2O3) is one of the most commonly used digestibility markers, but it is an unreliable passage marker because its physical properties and flow kinetics have little resemblance to the flow characteristics of any digesta fraction. 2 Chromium forms strong ligands with plant cell wall constituents, and Cr-mordanted fiber is used as a particulate flow marker. 7 Nonfiber substances are removed before binding in order to improve retention of Cr on the cell wall matrix. Concentration of Cr, however, dramatically increases the density and reduces digestibility of the labeled particles. It is...


The well-documented examples of drug-induced autoimmune-like syndromes have led to studies to determine whether certain agents contribute to the incidence of autoimmune diseases. Some of the chemical and therapeutic agents suggested to be associated with autoimmune diseases or autoimmune phenomenon (i.e. increased levels of autoantibodies), in experimental animals or humans are listed in Table 1 and include several heavy metals, pharmaceuticals, organic solvents and foods. As a number of factors participate in the development of autoimmune disease and it presents both diverse clinical symptomology and organ specificity, appropriate animal models have been difficult to develop. One method that has received attention is the popliteal lymph node assay (PLNA) which measures proliferative activity in the draining lymph nodes. Although this assay appears to detect low molecular weight compounds with immunomodulatory potential, it does not necessarily discriminate those that influence...


Arsenic is a nearly tasteless, odorless metal it is the most common cause of acute metal poisoning and the second leading source of chronic metal toxicity. Arsenicals are found in a variety of compounds and industries (see Iable17.8 1) and continue to be used as tools for homicides and suicides.


Diagnosis and etiology Emphysema means 'inflation' in the sense of abnormal distension with air. It is a condition in which there is permanent destructive enlargement of the airspace distal to the terminal bronchioles without obvious fibrosis. In the general population, emphysema usually develops in older individuals with a long smoking history. However, other causes include exposure to heavy metals such as cadmium, and 5 of early presenting cases are caused by the autosomal recessive disorder -antitrypsin deficiency. It affects almost 5 of older people, and it is more common in industrialised countries. The prognosis is variable. Progression is slow, provided it is treated.

Nonspecific immunity

A number of nonspecific host factors form an important first line of defense against fungal invasion. These include the mechanical barrier provided by the skin and mucous membranes, competition for nutrients from the normal indigenous bacterial flora, and the mucociliary clearance system of the respiratory tract. The importance of these factors is illustrated by the association of disseminated candidiasis with the disruption of mechanical barriers by burns, surgical wounds or intravenous catheters and with the inhibition of normal bacterial flora by broad-spectrum antibiotics. In serum, chelation of iron and other essential heavy metals restricts the growth of many fungi. The association of mucormycosis with therapy with the iron-chelator deferoxamine is thought to be due to the ability of the causative

Lipid Oxidation

The lipids of raw meat are initially protected from oxidation by endogenous antioxidants, but eventually these antioxidants are inactivated and the rancidity process starts. Exposure to light and heavy metals promotes the onset of rancidity. Rancidity, being initiated by a free-radical reaction, continues even in the absence of additional oxygen, so conditions to minimize its initiation are most important. Vacuum packaging is one option freezing is another. As all chemical reactions proceed more slowly at lower temperatures, meat should be stored at as low a temperature as practical.


Molasses is a byproduct of the sugar industry and readily available at relatively low cost. It contains water, sugars (sucrose, invert sugar, 50 w w), nitrogen compounds (betaine, glutamine, asparagine, leucine, isoleucine, alanine, valine, glycine, and nitrogen as nitrates and nitrites), organic acids, and heavy metals such as iron, zinc, copper, manganese, magnesium, and calcium (185). High heavy metal concentrations in molasses solution cause a

Residues in Foods

Through exposure from air, water, or land, a food supply may be contaminated with certain residues, which may eventually be consumed by humans. Some contaminations may be residues of compounds purposely used to protect crops from insects (insecticides) or destroy competing plants (herbicides). Other contaminations may be from industrial waste or pollution, by accident, ignorance, or recklessness. Some contaminations may be naturally found in the food supply, such as those derived from the soil as food plants are grown, e.g., some heavy metals. Residues or contaminants found in foods differ widely in chemical structure, but all possess toxic properties that may be a threat to human health. Some of these chemicals tend to accumulate in the food supply, being more toxic in higher-order mammals than in species of lower phylogenetic orders. For example, fish and crustaceans can tolerate much higher tissue levels of arsenic and mercury than can humans.


A blood testis barrier prevents some compounds in blood from entering the seminiferous tubules where sperm are produced. This prevents compounds such as heavy metals and drugs from damaging sperm. Mitotic and meiotic cell divisions occur during spermatogenesis. Spermatogonia undergo several mitotic divisions to become primary spermatocytes, which undergo meiotic divisions to become secondary spermatocytes, then spermatids, and finally spermatozoa or sperm. Spermatogenesis results in a multiplication in the number of sperm produced and a reduction in the genetic material in sperm to half the amount of other cells in the body (haploid).


If the edge of the element to analyze is close to the edge of the heavy metal used for tissue fixation and staining, elemental analysis of the structure may be difficult, because the signal from the structure may be overlapped by the signal of the heavy metal. In our experiment, the use of heavy metals for tissue fixation is inevitable to preserve all components of the inner lung surface. However, poststaining ultrathin sections with heavy metals for contrast enhancement is no longer necessary because energy filtering enables the generation of images with an enhanced contrast.


Biosorption is a term that describes the broad range of processes by which biomass removes metals (and other substances) from solution, yet it can also be used in a stricter sense to describe uptake by dead (detritus) or living biomass by purely physico-chemical processes such as adsorption or ion exchange (White et al. 1995). Metabolic processes inherent in living biomass may contribute to the uptake mechanism. Ideally a biosorbent has the ability to be recycled and the sorbed metal ions recovered for reuse or safer disposal. Choice of a suitable biotrap is at times made easier if certain genetic and biochemical characteristics of an organism are known. That fungi and yeast can serve as biotraps for heavy metals has been the subject of a great deal of research as evidenced by several prior reviews on the subject (Blackwell et al. 1995 Kapoor and Viraraghavan 1995 1997).

Protein A

Staphylococci frequently acquire resistance to various antibiotics. In hospital environments the vast majority of S. aureus strains produce ( -lactamase, and are resistant to various penicillins. Strains may acquire resistance to penicillinase-stable penicillins, such as methicillin, by incorporation of mec gene(s). These methicillin-resistant S. aureus strains, MRSA, may be resistant to several other antibiotics and to heavy metals, and constitute a serious problem in hospital hygiene. Methicillin-resistant coagulase-negative staphylococci, MRSE, may likewise be resistant only to penicillins or also to several other antibiotics. MRSE constitute an increasing problem in hospital hygiene.

Distillery Waste

As can be seen, the values of BOD and COD may vary significantly and may reach extremely high values of over 300 and more than 150 g l, respectively. The pH ranges from 3 to 5. The waste can contain different amounts of solids up to more than 400 g l. For cultivating microorganisms, the content of carbon and nitrogen sources is the most important factor. The ratio of C N varies with the raw material used for alcoholic fermentation. In addition to the components given in Table 1, there are different amounts of organic and amino acids, polyols, vitamins, phenolics, etc. Minerals include potassium, phosphorus, sulfates, and some heavy metals. These components may also have an important influence on


Adsorption of anions and cations Although physical binding (adsorption) of anions and cations occurs at the surface of both mucilaginous and non-mucilaginous algae, recent studies have shown that algae with a large amount of mucilage tend to have a higher capacity for ion adsorption. This has potential significance for the uptake of nutrients from the aquatic environment and the ability of algal cells to resist heavy-metal toxicity.


They are neither created nor destroyed (neglecting nuclear reactions), yet they readily change form and activity. A subgroup in which we are most interested is the heavy metals. Heavy metals are those with atomic number 22 to 34 and the elements below them in the periodic table, plus the lanthanides and actinides. Metals are widely and unevenly dispersed in the environment. Human activities that result in exposure to significant amounts of metals include mining and smelting operations, metal plating, fuel combustion, leather tanning, and their use in products from pigments to pipes.


Was originally discovered as a cytoplasmic heavy-metal-binding protein, which was thought to prevent metal toxicity within cells. Additional more significant roles were suggested by the realization that there are multiple MT genes, which have been conserved through evolution. It is a small protein that is unusually rich in cysteine and can bind seven atoms of zinc. MT may influence the subcel-lular distribution and availability of zinc, since its own distribution varies. For example, the nuclear content of MT varies with the cell cycle. MT expression is regulated not only by heavy metals but also by a range of other signals including glucocorticoids, interleukins, and cyclic adenosine monophosphate. In addition, its zinc-binding activity is influenced by the cellular redox state. For example, an increase in the glutathione disulfide-glutathione ratio results in the release of zinc from MT and thus an increase in its availability for other proteins. However, deletion of individual MT...

Vaginal Bleeding

The most common cause of fetal wastage is chromosomal abnormalities, accounting for 50 to 60 percent of all losses. Other risk factors include advanced maternal age, prior poor obstetric history, concurrent medical disorders, previous abortion, certain infections, including syphilis and HIV, and some anatomic abnormalities of the upper genital tract. Exposure to some agents, such as certain anesthetic agents, certain heavy metals, and tobacco, is also thought to contribute to the incidence of abortion.

Laboratory Studies

Laboratory studies help to rule out potentially reversible causes of dementia. Initially, the literature suggested that reversible dementias occurred in 10-15 of cases however, recent reports have pointed to a lower frequency (35-38). The practice parameters of the American Academy of Neurology (14) recommend that a workup include the following complete blood count, electrolytes, calcium, glucose, BUN, creatinine, liver function tests, thyroid function tests, B12, and syphilis serology. Many would also include a sedimentation rate, urinalysis, and chest radiograph. A patient's history should help guide other tests that may need to be ordered. For example, a patient with a long history of smoking should have a chest radiograph if none has been done recently. Someone with a history of high-risk sexual behaviors or exposure to intravenous drugs should have HIV testing. Patients who may have been exposed to industrial toxins at work should be considered for 24-hour urine collection for...


After absorption, cadmium binds to the protein metallothionein in cells of the intestinal tract wall and in the liver. Metallothionein is a key protein that contributes to the homeostasis of essential zinc and copper and in the detoxification of heavy metals. If people do not eat foods that contain enough iron or other nutrients, they are likely to take up more cadmium than the usual from their food. The general population and people living near hazardous waste sites may eat or drink cadmium in food, dust, or water.

Multiple Births

See also Alcohol Absorption, Metabolism and Physiological Effects. Ascorbic Acid Physiology, Dietary Sources and Requirements. Caffeine. Diabetes Mellitus Etiology and Epidemiology Classification and Chemical Pathology Dietary Management. Early Origins of Disease Fetal. Folic Acid. Food Safety Other Contaminants Heavy Metals. Hypertension Etiology. Iodine Physiology, Dietary Sources and

Gender and age

In addition to the toxicity differences that can occur between genders, several other hormone-dependent effects influence the toxicity of compounds. Pregnancy markedly increases the susceptibility of animals to pesticides, and lactating animals are more susceptible to heavy metals. Hyperthyroidism and hyperinsulinism may alter the susceptibility of animals and humans to toxicants.

Fruit Extracts

Contains large amounts of heavy metals which are removed by treatment of syrup with cation exchange resin, sulfuric acid, tricalcium phosphate, potassium ferrocyanide, and EDTA (105,206,207). Al-Obaidi and Berry (207) applied a filtration technique to produce citric acid from date syrup. In this process the medium was exchanged using an external filtration loop in which only a small percentage of the medium passing through the upper chamber of the filter was removed at any one pass. In this way cells were maintained suspended in the growth medium throughout the filtration process. Using this technique, the maximum citric acid concentration and the yield were 102.0 g L and 72.2 , respectively. Roukas and Kotzekidou (105) studied the production of citric acid from date syrup and found that the maximum citric acid concentration (55.0 g L), citric acid yield (50.0 ), and sugar utilization (73.0 ) were obtained in medium treated with 2 tricalcium phosphate. The optimum pH for citric acid...

Septic tank

Although it is convenient to consider the food and beverage industry as a single group, the effluent produced is extremely variable in composition, depending on the specific nature of the business and the time of the year. However, there are some consistent factors in these effluents, one of which being their typically heavy potassium load. Much of their nutrient component is relatively readily available both for microbial metabolism and plant uptake, which obviously lends itself to rapid utilisation and in addition, the majority of effluents from this sector are comparatively low in heavy metals. Inevitably, these effluents typically contain high levels of organic matter and nitrogen and, consequently, a low C N ratio, which ensures that they are broken down very rapidly by soil bacteria under even moderately optimised conditions. However, though this is an obvious advantage in terms of their treatability, the concomitant effect of this additional loading on the local microbiota has...


Hormone deficiency or excess Natural toxins Heavy metals Solvents Although teratogenesis is classified here with genotoxic effects, its causes are not well understood, and a number of other mechanisms probably also act. It seems that anything that interferes with cell division can be a teratogen. This includes agents known to block DNA expression, heavy metals such as lead and cadmium that inhibit enzymes, and even substances that simply cause a delay in cell replication.

Types of Plasmids

Plasmids are not usually required by their host cell for its survival. Instead, they carry genes that confer a selective advantage on their host, such as resistance to heavy metals or resistance to naturally made antibiotics carried by other organisms. Alternatively, they may produce antibiotics (toxins) that help the host to compete for food or space. For instance, antibiotic resistance genes produced by a plasmid will allow its host bacteria to grow even in the presence of competing bacteria or fungi that produce these antibiotics.