Pesticide Pollution and Natural Ecosystems

Effect on the Soil Environment

Many pesticides contain chemicals that are persistent soil contaminants; their effects may last for years. Pesticides move with water in soil to groundwater and on soil to surface water. They decrease biodiversity in the soil by killing soil organisms; when life in the soil is killed off, the soil quality deteriorates and has a knock-on effect upon the retention of water. This is a problem for farmers particularly in times of drought.1101 At such times, organic farms have been found to have yields 20%-40% higher than conventional farms. Soil fertility is affected in other ways, too. When pesticides kill off most of the active soil organisms, the complex interactions that result in good fertility break down. Risk assessment of pesticide impact on human health is not an easy and particularly accurate process because of difference in the periods and the levels of exposure types of pesticides mixtures in the field and geographic and meteorological characteristics of the agricultural area of pesticide applied.111*121 The data is usually collected from various tests conducted on metabolism patterns, acute toxicity, subchronic, chronic, car- cinogenecity, genotoxicity, teratogenecity, and generation study using rat as a model mammal or dogs and rabbits.1131

Application of systemic pesticides as drenches or granules may exhibit indirect effects on natural enemies via several mechanisms including elimination of floral parts by consumption of active ingredient while ingesting plant fluids and contamination of prey ingesting either lethal or sublethal concentration.114-161

Plants depend on millions of bacteria and fungi to bring nutrients to their rootlets. When these cycles are disrupted, plants become more dependent upon exact doses of chemical fertilizers at regular intervals. Even so, the incredibly rich interactions in healthy soil cannot be fully replicated by the farmer with chemicals. Hence, the soil and our nutritionist compromised. We get large but watery vegetables and fruits, which often lack natural taste and nutrients and may even contain harmful toxic pesticide residues. Studies of pesticide effects on the soil fauna have reported increased numbers of collembolan, because chemicals reduced populations of natural enemies, especially of predatory mites.1171

Effect on the Aquatic Environment

Pesticides enter the freshwater ecological systems either from direct application of pesticides for the control of harmful aquatic fauna or as runoff from the treated areas, drift during aerial spraying, and industrial effluents from washing and spraying of equipment and containers. Several groups of organo- chlorine pesticides such as DDT, endosulfan, and chlorinated phenoxy acetic acid used as herbicides and fungicides such as hexachlorobenzene and pentachlorophenol are of interest in water pollution. Because of their solubility in water and tendency to be absorbed on solid surfaces, only traces of these chemicals are found in solid surfaces and treated water.118!

Microorganisms form a vital part of the freshwater environment. Bishop119! measured the effects of DDT on Mastigophora, Infusoria, and Sarcodina in ponds near Savannah, Georgia, and found little change in population numbers after treatment at relatively low rates. Hoffman and Olive1201 found that the growth of populations in Colorado lakes was inhibited after the addition of rotenone and toxaphene. Phytoplankton (beneficial/detrimental) can be seriously affected by agricultural chemicals. DDT sprays have caused serious reductions of bottom-dwelling invertebrates, the reductions in some cases amounting to 95% of the population. Malathion has also caused destruction of stream invertebrates. Cushing and Olive121! found that toxaphene and rotenone reduced numbers of midge larvae in Colorado reservoirs and algae. On higher plants in the freshwater environment, adsorption of pesticides in/on the vegetation resulted in phytotoxicity, which either retarded the growth of or killed aquatic plants. Kolleru Lake is the largest natural freshwater body of Andhra Pradesh in India where agriculture and aquaculture are some of the primary activities at the lake basin. The increased use of pesticides in agriculture and aquaculture had a negative impact on the quality of water in the lake.122*231

A major environmental impact has been the widespread mortality of fish and marine invertebrates due to the contamination of aquatic systems by pesticides. 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. In addition, 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. Some pesticides, such as pyre- throids, are extremely toxic to most aquatic organisms. It is evident that pesticides cause major losses in global fish production.

Effect on the Terrestrial Environment

A wide variety of pesticides are applied on horticultural and agricultural crops. Some of them are highly specific and others are broad spectrum; both types can affect terrestrial wildlife, soil, water systems, and humans. The misuse of pesticides can cause valuable pollinators such as bees and hoverflies to be killed, and this in turn can badly affect food crops. Bees are extremely important in the pollination of crops and wild plants; about 33% of all crops require pollination. 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. Bee population has been suffering a serious decline in recent years. Without bees, many food crops would simply fail to grow.

Neonicotinoid pesticides developed in 1980 are under fire for risks to pollinators, and European Union Commission had already imposed this class of pesticides as researchers have become concerned about their potential to harmless birds, earthworms, aquatic insects, and pollinators.1241 Three neonicotinoids—thiamethoxam, clothianidin, and imidacloprid—posed an unacceptable risk to bees and were banned for use for some period on flowering crops such as corn, oilseed rape, and sunflower upon which the bees feed.1251

It has been observed that through natural selection, some pests eventually become quite resistant to pesticides and farmers may need increasing amounts of pesticides, making the problem worse. Orchards are complex ecosystems easily perturbed by the extensive use of pesticides, and there are many instances of increased pest attacks in orchards after the use of pesticides, e.g., outbreaks of codling moth, lea- frollers, aphids, scales, and tetranychid mites.1261 When pesticides were first used on tropical cotton crops, they controlled two or three important pests of the crops and greatly increased yields. Within a few seasons, however, the chemicals reduced the population of natural enemies and a number of other arthropod species became pests.1271

Amphibians such as frogs are particularly vulnerable to concentrations of pesticides in their habitat. Atrazine, the most heavily used herbicide, is regularly detected in drinking water supplies in the Midwest, the United States, and exposure to extremely low levels of atrazine can cause sex change and/ or deformities in frogs, fish, and other organisms.1281 Based on this evidence, and the widespread presence of atrazine in drinking water supplies, the European Union (EU) announced a ban on atrazine in 2006. The US Environmental Protection Agency re-registered atrazine in 2003 despite objections from scientists and environmental groups.

Pesticides 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 of organochlorine insecticides through terrestrial food chains. Pesticides may kill grain- and plantfeeding 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. Pesticides can affect animal reproduction directly, as evident by the deleterious effect of the persistent organochlorine insecticides on reproduction in receptors and other birds. The US National Academy of Sciences stated that the DDT metabolite, dichlorodiphenyldichloroethane (DDE), causes eggshell thinning and that the bald eagle population in the United States declined primarily because of exposure to DDT and its metabolites.1291 Fish-eating birds are more severely affected than terrestrial predatory birds, because the former acquire more pesticides via their food chain.1301 Pesticides can also affect reproduction in invertebrates, e.g., sublethal doses of DDT, dieldrin, and parathion increased egg production of Colorado potato beetle after 2 weeks by 50%, 33%, and 65%, respectively.1311 Aquatic ecosystems with flowing water can usually recover their structure and function more quickly from pesticide effects than ponds with standing water.

Effects on Humans

There are a number of ways in which humans can be exposed to pesticides through the environmental route. Man’s primary exposure to pesticides is probably via those used domestically in wood preservation or as household insecticides. Pesticides can endanger workers during production and transportation or during and after use. Bystanders may also be affected at times, e.g., walkers using public rights-of-way on adjacent land or families whose homes are close to crop-spraying activities. One of the main hazards of pesticide use is to farm workers and gardeners. A recent study by the Harvard School of Public Health in Boston discovered a 70% increase in the risk of developing Parkinson’s disease for people exposed to even low levels of pesticides.1321

The effects of pesticide residues in food and water probably cause a great public concern, although reports of clinical poisoning due to residues are extremely rare. Their residual population in food commodities is alarming. Leafy vegetables, cereals, fruits, rice, meat, milk, fish, and even human milk have been contaminated by various pesticides in a range of 0.1-25.7 mg/kg. The herbicide 2,4-D is identified as a carcinogen in humans and dogs. Acephate is a mutagen, carcinogen, fetotoxic, feminizes rats, and kills birds. In a multicountry study (Belgium, China, Federal Republic of Germany, India, Israel, Japan, Mexico, Sweden, the United States, and Yugoslavia) on the assessment of human exposure to selected organochlorine compounds, the residue levels for pp’-DDE and P-HCH were found to be higher in the human milk samples collected from developing countries such as China, India, and Mexico than in the participating developed countries. A higher level of these chemicals in mother’s milk is a clear-cut reflection of their increased burden through their translocation passage.1331

A number of bottles of wine were tested for pesticide residues, and 100% of conventional wines included in the analysis were found to contain pesticides, with one bottle containing ten different pesticides. On an average, each wine sample contained more than four pesticides. The analysis revealed 24 different pesticide contaminants, including five classified as being carcinogenic, mutagenic, neurotoxic, or endocrine disrupting by the EU. Human health is at risk when chemical residues are present in so much of our food supplies.

Children are particularly vulnerable to the toxic effects of pesticides. Studies have found higher rates of brain cancer, leukemia, and birth defects in children who suffered early exposure to pesticides. A survey of baby foods in 2000 showed detectable pesticide residues in nearly 50% of foods sampled. Fourteen percent of foods tested showed residues of more than one pesticide at levels 30 times the proposed limit of 0.01 mg/kg.1341 A UK government report in 2003 showed that more than 70%, 90%, 61%, 54%, and 35% of apples, lemons, bread, rice, and potatoes analyzed had pesticide residues, respectively. The main source of exposure to pesticides for most people is through diet. A study in 2006 measured organophosphorus levels in 23 school children before and after changing their diet to organic food. The levels of organophosphorus exposure dropped immediately and dramatically when the children began the organic diet.1341

Over the last few decades, agricultural pesticides have become common household items in rural areas of the developing world. In 2014, the Natural Crime Records Bureau of India reported 5650 farmer suicides.1351 In India, the first report of poisoning due to pesticides was from Kerala in 1958, where more than 100 people died after consuming wheat flour contaminated with parathion.1361 This prompted the Special Committee on Harmful Effects of Pesticides constituted by the Indian Council of Agricultural Research to pay more attention on the problem.1371 Exposure to accidental emissions of methyl isocyanate from a pesticide factory in Bhopal, India, killed more than 5000 people, leaving more than 50,000 with permanent damage.

Alternatives for Pesticide Problems

The toxic effects of pesticides on our foods, land, and their effects on the health of human beings and their progeny make it an issue that is becoming more and more crucial. Integrated pest management (IPM; pest surveillance, use of crop varieties resistant to pest, sound cultural practices, biological control, and use of ecofriendly pesticides) emphasizes the need for simpler and ecologically safer measures for pest control to reduce environmental pollution and other problems caused by excessive and indiscriminate use of pesticides. Preference should be given to organic foods that are grown without toxic pesticides by organic methods. There are now many biological control tactics available where benign species are used to manage less benign ones. Ladybirds (ladybugs) are often introduced to control aphids (greenfly and others). Organic nontoxic sprays are used to stimulate the soil. They work by stimulating fungi in the soil that help to feed the plants and help them in developing resistance to disease and insect attack. There are also many successful barrier methods that help to deter insect attacks (the use of nets to ward off birds and larger insects). Companion planting is also used; garlic, for example, helps some plants resist insect attacks. There are a small number of organic pesticides that are legitimate to use in organic food production system. Some of these can be made at home using simple ingredients such as soap and alcohol.

It is evident that misuse, overuse, and abuse of pesticides lead to many environmental problems as discussed. Pesticides must be used as part of a planned systematic pest management program utilizing as many control techniques as applicable (IPM).

Novel pesticides’ modes of action, improved safety profiles, and the implementation of alternative cropping systems which are less dependent on pesticides could minimize exposure to pesticides and undesirable exposure on human health. Moreover, the use of appropriate and well-maintained spraying equipment along with taking all the precautions required in all the stages of pesticide handling could also reduce exposure to pesticides. The overall pesticide handling according to regulations reducing the public concerns in food and drinking water minimize the effects of pesticides in human health and environment.1381

Emphasis should be placed on using all the techniques of organic farming and supplementing these with the use of pesticides, i.e., using pesticides as part of an organic farming system. The IPM approach will help to minimize the effects of pesticide pollutants on the environment and natural ecosystems and will also help in economic and ecological sustainable food production.


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