Effects Of Toxic Pollutants On Food Chains Environmental Sciences Essay

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1st Jan 1970 Environmental Sciences Reference this


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When a factory pours harmful chemicals or wastes into the air or water, when oil leaks from a burning oilrig or when a tanker runs aground, and when a farmer puts pesticides or fertilizers on a field to increase crop yield, it is said that these things pollute the environment. Pollution can take many forms. Its effects can have a major impact on food chains both in the water and on the land.  Everything from plants to animals, large and small is impacted. Pollutants like oil, pesticides, fertilizers such as nitrogen and phosphate from fertilizers, and lead can have a tremendous impact on the ecosystem, especially if the water gets polluted.

Effects of Toxic Pollutants on Food Chains

An ecosystem can be defined, as a self-contained, dynamic system made of a population of species in its physical environment. The study a community is complex and includes the interactions between the organisms that make it up, and include: plants, animals, bacteria, and fungi. There are many different ways in which the community of organisms interacts. First is the food chain, where each organism is in a producer, consumer, predator, and prey relationship (Smith, Walker, et al). Next are the oxygen and water cycles that sustain the organisms. They provide the raw materials necessary for photosynthesis and cellular respiration, which make energy, and in turn, use it. When an ecosystem gets polluted, the natural balance in the system is disturbed, affecting the organisms in different ways. It is important to know how a simple act like introducing sewage water or toxic waste into a lake can threaten several animal and plants species in the area.

Pollutants like oil, pesticides, nitrogen and phosphate from fertilizers and lead can have a tremendous impact on the ecosystem, especially if the water gets polluted. In a lake, for example, it can change the ecological balance by stimulating plant and algae growth, causing the death of fish due to suffocation from the lack of oxygen dissolved in the water. The oxygen cycle will eventually stop. The polluted water will also have a significant affect the animals’ dependant on the lake water. With no food to eat, or water to drink, they will be forced to move to another area, or face death.

Both the Deepwater Horizon oil spill in the Gulf of Mexico in 2010 and the Exxon Valdez Spill in Alaska in 1989 caused significant damage to marine and wildlife habitats. In the Gulf of Mexico, it is reported that balls of oil continue to wash up along the shore, while dredging has shown mats of oil resting on the ocean floor, and oil sheen trails are still seen in the wake of fishing boats (CBS). Wetlands marsh grass remains fouled and dying, and oil can be seen in the pore space of sand and gravel deposits along the estuary edges of the Gulf. Although there was an extensive use skimmer ships, containment booms, raking of beaches and chemical and biological remediation (by introducing oil eating bacteria to “eat” the oil), the dispersion of the pollutants seems to have had minimal effect. In the short term, after several months, the fishing industry was allowed to resume operations (although in some areas, oil balls are found in the fishing nets). It is, however, too soon to know what the long terms effects will be.

In Prince William Sound, Alaska, the use of a detergent dispersant had little effect and was stopped when it was found to be toxic to the cleanup workers and native wildlife. Wave action, which is important to disperse the oil in the water, was not enough, and the process was stopped (MacAskill). Attempts to burn the oil away, on a small scale, were successful, but had to be stopped when the weather changed. Ecosystems here form the basis of the coastal food chains. Animal life impacted by the spill included aquatic mammals, fish, birds as well as their related food chains. In the short term, hundreds of thousands of mid- and upper-level food chain animals were impacted, along with future generations (the eggs laid by salmon), for example, and in the long-term, scientists are still seeing contamination which has lead to a drastic reduction in populations across the board (Gill & Elliott). Living in upstate New York, the use of nitrogen- and phosphorus-based fertilizers to increase crop yield are commonplace. The chemicals and nutrients found in them, while beneficial for agricultural crops can be lethal in high doses for fish, birds and other wildlife. Pesticides, designed to kill pests chemically, are also dangerous when leached into soil or groundwater supplies. Heavy amounts of fertilizer chemicals like potassium, nitrogen and phosphorus in natural water systems can actually cause “dead zones” where wildlife cannot survive because of lower oxygen levels and chemical poisoning. Insects and organisms like honeybees and soil microbes that are beneficial to the food chain can be killed alongside the pests, eliminating that part of the ecosystem that is beneficial to crop health and sustainability. Nitrate (NO3) is a naturally occurring form of nitrogen found in soil. Nitrogen is essential to all life, and most crop plants require large quantities to sustain high yields. The formation of nitrates is an integral part of the nitrogen cycle in the environment. In moderate amounts, they are a harmless constituent of food and water. Plants use nitrates from the soil to satisfy nutrient requirements and may accumulate nitrates in their leaves and stems (Relyea). Due to its high mobility, nitrates can also leach into groundwater, where ingestion can cause rare illness such as methemoglobinemia (found especially in infants) to occur. Nitrates form when microorganisms break down fertilizers, decaying plants, manures or other organic residues. Plants naturally take up these nitrates, but rain and irrigation water can cause them to runoff into lakes or streams, or leach them into groundwater. Although nitrate occurs naturally in some groundwater, in most cases higher levels are thought to result from human activities (Relyea). Common sources of nitrate include: fertilizers and manure, animal feedlots, municipal waste and sludge, septic systems and natural nitrogen fixation conducted by legumes, bacteria, and lightning.

Nitrates that enter the food chain through non-natural means can have serious, and sometimes long-lasting effects on both plants and animals. Cattle and sheep (ruminants) are susceptible to nitrate poisoning when they drink contaminated water, animal feed or fodder. To protect drinking water, it is important to limit the loss of excess water and plant nutrients, and match fertilizer and irrigation applications to precise crop uptake needs in order to minimize groundwater contamination. While it may be technically possible to treat contaminated groundwater, it can be difficult, expensive and not totally effective. For this reason, prevention is the best way to ensure clean water. Water treatments include distillation, reverse osmosis, ion exchange or blending. Phosphorus is another common constituent of agricultural fertilizers, manure, and organic wastes in sewage and industrial effluent. It is an essential element for plant life, but when there is too much of it in water, it can speed up eutrophication (a reduction in dissolved oxygen in water bodies caused by an increase of mineral and organic nutrients) of rivers and lakes. Soil erosion is a major contributor of phosphorus to streams. Bank erosion occurring during floods can transport a lot of phosphorous from the riverbanks and adjacent land into a stream. It gets into water in both urban and agricultural settings, tends to attach to soil particles and, moves into surface-water bodies from runoff. A United States Coast and Geological Survey (USGS) study on Cape Cod, Massachusetts showed that phosphorus could also migrate with ground-water flows (Perlman). Since ground water often discharges into surface water, such as through stream banks into rivers, there is a concern about phosphorus concentrations in ground water affecting the water quality of surface water.

Pesticides are substances or a mixture of substances, of chemical or biological origin, used by human society to eliminate or repel pests such as bacteria, nematodes, insects, mites, mollusks, birds, rodents, and other organisms that affect food production or human health (Pimentel). They usually act by disrupting some component of the pest’s life processes to kill or inactivate it. In a legal context, pesticides also include substances such as insect attractants, herbicides, plant defoliants, desiccants, and plant growth regulators. They can have an effect on both the water and soil. These pollutants have had some of their most striking effects on birds, particularly those in the higher trophic levels of food chains, such as bald eagles, hawks, and owls. These birds are often rare, endangered, and susceptible to pesticide residues such as those occurring from the bioconcentration (the amount of solute per unit volume of solution) of organic, chlorine-based insecticides through land-based food chains. Pesticides may kill grain- and plant-feeding birds, and the elimination of many rare species of ducks and geese has been reported. Populations of insect-eating birds such as partridges, grouse, and pheasants have decreased due to the loss of their insect food in agricultural fields through the use of insecticides. Bees are extremely important in the pollination of crops and wild plants, and although pesticides are screened for toxicity to bees, and the use of pesticides toxic to bees is permitted only under stringent conditions, many bees are killed by pesticides, resulting in the considerably reduced yield of crops dependent on bee pollination. The movement of pesticides into surface and groundwater happens through the processes of infiltration (when water sinks into unsaturated layers of soil) and runoff. Wildlife is affected, and human drinking water is sometimes contaminated beyond acceptable safety levels. In Beekman, New York, pesticides used to kill an infestation of insects in a public school lead to the contamination of the village water supply when it leached into the reservoir. Sediments dredged from U.S. waterways are often so heavily contaminated by pesticide residues that it becomes hard to safely dispose of them on land. A major environmental impact has been the widespread death of fish and marine invertebrates due to the contamination of aquatic systems by pesticides. This has resulted from the agricultural contamination of waterways through fallout, drainage, or runoff erosion, and from the discharge of industrial wastes into waterways. Historically, most of the fish in Europe’s Rhine River were killed by the discharge of pesticides, and at one time fish populations in the Great Lakes became very low due to pesticide contamination (Smith). Many of the organisms that provide food for fish are extremely susceptible to pesticides, so the indirect effects of pesticides on the fish food supply may have an even greater effect on fish populations. It is evident that pesticides cause major losses in global fish production, as they are extremely toxic to aquatic organisms. The literature on pest control lists many examples of new pest species that have developed when their natural enemies are killed by pesticides. This has created a further dependence on pesticides not very different from drug dependence. Finally, the effects of pesticides on the biodiversity of plants and animals in agricultural landscapes, whether caused directly or indirectly by pesticides, constitute a major adverse environmental impact of pesticides.


As chemicals diffuse up through the food chain, the top-level predators end up with the highest concentration of the chemicals in their bodies, and suffer the worst effects. They can have a major impact on all levels of the food chain. Excessive levels of pollution are causing a lot of damage to human and animal health, plants and trees, including tropical rainforests, as well as the wider environment. All types of pollution, air, water and soil, have an impact on the living environment. The effects in living organisms may range from mild discomfort to serious diseases such as cancer or physical deformities (extra or missing limbs in frogs). Experts admit that pollution effects are quite often underestimated and that more research is needed to understand the connections between pollution and its effects on all life forms. Waterborne diseases caused by polluted water can include: typhoid, amoebiasis, giardiasis, scariasis, hookworm, rashes, ear ache, pink eye, respiratory infections, hepatitis, encephalitis, gastroenteritis, diarrhea, vomiting, and stomach aches. Conditions related to water polluted by chemicals (such as pesticides, hydrocarbons, persistent organic pollutants, heavy metals etc) can include: cancer (prostate cancer and non-Hodgkin’s lymphoma), hormonal problems that can disrupt reproductive and developmental processes, damage to the nervous system, liver and kidney damage, damage to the DNA, and exposure to mercury (heavy metal). Soil pollution has many effects, as well, including: cancer, and leukemia. Lead in soil is especially hazardous for young children causing developmental damage to the brain. Mercury can increase the risk of kidney damage; cyclodienes (an organic insecticide) can lead to liver toxicity. Other effects can include neuromuscular blockage, depression of the central nervous system, headaches, nausea, fatigue, eye irritation and skin rash.


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