Food-chain

The effects of pollution can be direct, such as toxic emissions providing a fatal dose of toxicant to fish, animal life, and even human beings. The effects also can be indirect. Toxic materials which are nonbiodegradable, such as waste from the manufacture of insecticides and pesticides, if released to the environment, are absorbed by bacteria and enter the food chain. These compounds can remain in the environment for long periods of time, slowly being concentrated at each stage in the food chain until ultimately they prove fatal, generally to predators at the top of the food chain such as fish or birds. 

Plants, in contrast to animals, have the ability to convert carbon dioxide from the atmosphere and inorganic components of the earth direcdy into high energy carbohydrates (qv), fats, and proteins (qv). These plant materials are absolutely essential to human nutrition as well as to the nutrition of other animal species. Thus consumption of plant matter, either directly or through a food chain, is essential to animal life and humans are totally dependent on agricultural endeavors, ie, the culture and harvesting of plant matter. 

DDT is highly toxic to fish (LC q for trout and blue gill, 0.002—0.008 ppm), and it is only moderately toxic to birds (oral LD q mallard 1300 and pheasant >2240 mg/kg). However, widespread bird kills have resulted from bioconcentration of DDT through food chains, ie, from fish or earthworms. A significant environmental problem has resulted from the specific effects of DDE on eggshell formation in raptorial birds where accumulation has caused decreases in shell thickness of 10—15%, resulting in widespread breakage. 

Conduct Hazard Analysis and Risk Assessment. Ahazardis any biological, chemical, or physical property that may cause an unacceptable consumer health risk. AH of the potential hazards in the food chain are analyzed, from growing and harvesting or slaughtering to manufacturing, distribution, retailing, and consumption of the product. 

Exposure. The exposure of humans and animals to mercury from the general environment occurs mainly by inhalation and ingestion of terrestrial and aquatic food chain items. Pish generally rank the highest (10—300 ng/g) in food chain concentrations of mercury. Swordfish and pike may frequently exceed 1 p.g/g (27). Most of the mercury in fish is methyl mercury [593-74-8]. Worldwide, the estimated average intake of total dietary mercury is 5—10 p-g/d in Europe, Russia, and Canada, 20 pg/d in the United States, and 40—80 pg/d in Japan (27). 

Some metals used as metallic coatings are considered nontoxic, such as aluminum, magnesium, iron, tin, indium, molybdenum, tungsten, titanium, tantalum, niobium, bismuth, and the precious metals such as gold, platinum, rhodium, and palladium. However, some of the most important poUutants are metallic contaminants of these metals. Metals that can be bioconcentrated to harmful levels, especially in predators at the top of the food chain, such as mercury, cadmium, and lead are especially problematic. Other metals such as silver, copper, nickel, zinc, and chromium in the hexavalent oxidation state are highly toxic to aquatic Hfe (37,57—60). 

Concern over contaminants entering the food chain through fertilizer removed the first option. Increased cost and regulation has all but removed the second. Thus concentration, or recycling, has become more attractive and ia many cases even a necessity. 

In order to prevent veterinary dmgs from being transported to the human food chain, radioisotopic immunoassays were developed to monitor veterinary antibiotics such as penicillin and chloramphenicol [56-75-7] C22H22Cl2N20, in meat, milk, and eggs (qv) (see ANTIBIOTICS Meatproducts Milk AND MILKPRODUCTS). 

Environmental problems associated with PCBs are the result of a number of factors. Several open uses of PCBs have resulted in thein direct introduction into the environment, eg, organic diluents careless PCB disposal practices have resulted in significant releases into aquatic and marine ecosystems higher chlorinated PCBs are very stable in thein persistence in different environmental matrices and by a variety of processes (Fig. 1) PCBs are transported throughout the global ecosystem and preferentiaHy bioconcentrate in higher trophic levels of the food chain. 

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) ai e toxic compounds of anthropogenous origin, able to accumulate in tissues of alive organisms and to cause different diseases. These compounds ai e the most dangerous for aquatic ecosystems as they easily adsorb in sludge and ai e included in food chains of biota. Humans consume PCBs and OCPs mostly with fish. 

Exposure of wildlife to EDs also occurs via their food and in most ecosystems there is a tendency for persistent chemicals to bioaccumulate and biomagnify organisms higher up the food chain accumulate more of the chemical than those... 

It is also important to develop an understanding of the movement of chemicals through the environment by investigating their fate and behaviour. Based on a chemical s inherent physicochemical properties, it is possible to predict with some degree of certainty which environmental compartment it is likely to reside in and to what extent it is likely to be bioavailable and accumulate through the food chain. 

Bioconcentration, Bio accumulation and Biomagnification. These aspects are determined by the physicochemical properties of a chemical, an organism s ability to excrete the chemical, the organism s lipid content and its trophic level. Bioconcentration relates to the difference between the environmental concentration and that of the body tissues. A high bioconcentration factor (BCF) predisposes to bioaccnmulation. The upper limit of bioaccnmulation is determined by lipid levels in the organism s tissues. Whether the resultant body burden causes biomagnification in the food chain depends upon the metabolic capabilities of the exposed organism. 

Temperature also affects production rates but, through its influence on the thermal expansion of water, it also induces changes in the depth of vertical mixing and resistance to wind-stirring processes. Reactions to temperature of other components of the food chain are also important in the regulation of phytoplankton biomass by consumers. Different phytoplankton species, with important morphological differences, are differentiated selectively by the interplay of these factors. " ... 

Careful attention should be paid to processing and storage equipment to assure that certain future uses will not be contraindicated based upon the nature of the products. For example, it would not be wise to allow storage of food or food chain materials in vessels that once contained agricultural chemicals, even if the vessels were first cleaned. In the event the toller will not assure appropriate future use of the equipment, the client may consider purchasing the equipment for future use elsewhere. 

The movement of fluoride through the atmosphere and into a food chain illustrates an air-water interaction at the local scale (<100 km) (3). Industrial sources of fluoride include phosphate fertilizer, aluminum, and glass manufacturing plants. Domestic livestock in the vicinity of substantial fluoride sources are exposed to fluoride by ingestion of forage crops. Fluoride released into the air by industry is deposited and accumulated in vegetation. Its concentration is sufficient to cause damage to the teeth and bone structure of the animals that consume the crops. 

Important intermedia transfer mechanisms affecting soil contaminants include volatilization or resuspension to the atmosphere and biouptake by plants and soil organisms. These, in turn, introduce contaminants into the food chain. 

CHLORINATED HYDROCARBONS Hydfoearbons containing ehlorine atoms, e.g. triehloroethylene. Some of these ehemieals aeeumulate in the food chain and do not readily degrade. Some plastics which contain certain chlorinated hydrocarbons release dioxins into the ah, when burnt at low temperatures. 

Tetratchloroethylene has been detected in the food chain as a contaminant its volatility prevents significant bioaccumulation but some transfer to aquatic sediments is possible. At low concentrations it is slowly degraded under anaerobic conditions. 

There are concerns that land application of sludge will result in an increase of pathogenic bacteria, viruses, parasites, chemicals and metals in drinking water reservoirs, aquifers, and the food chain. This raises additional concerns of cumulative effects of metals in cropped soils. Research shows that if metals such as zinc, copper, lead, nickel, mercury, and cadmium are allowed to build up in soils due to many applications of sludges over the years, they could be released at... 

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