The Effect of Pesticides on Water Quality

By Jessica Kuhr (Geology), Mallory Larcom (NRC), and Laura Noe (Animal Science)

Agricultural Pesticides: Worth the Risk?

Limoeiro do Norte, Brazil, was once known only for its poverty— but in the 1990’s, the town was dragged up from destitution by an influx of agricultural industry. The growth of farming in this remote countryside city brought new jobs and fresh starts to the people who lived there, however there were darker side effects as well. July of 2008 marked the beginning of a descent into hell for one citizen of Limoeiro do Norte and his family. Vanderlei Matos da Silva, an employee of  Fresh Del Monte Produce, began to complain of headaches, fever, and jaundice that summer, and his condition continued to deteriorate in the following months, making him unable to work and eventually forcing him into a hospital in the city, miles away from his home and family (Prada, 2015).

By the time his wife and infant son were ringing in a new year, Silva had succumbed to multiple organ failure and hemorrhaging; a man who had been a healthy, loving father and husband less than six months before now lay dead after a long and painful fight for his life. Fresh Del Monte Produce was taken to court by Silva’s widow, and testimony began to unravel a story of hazardous working conditions and cover-ups, as well as the use of a pesticide which, though legal in Brazil, has been banned in numerous countries and it considered to be “highly poisonous” by the U.S. Centers for Disease Control. In 2013, five years after the death of Vanderlei Matos da Silva, Fresh Del Monte Produce was ordered to pay $110,000 in damages to his widow to atone for her husband’s untimely death (Prada, 2015).

The Impact of Pesticides

Rural farm workers aren’t the only ones to face the negative effects of pesticide use in agriculture, though. Studies have found that aquatic ecosystems and the organisms that make them up also suffer from exposure to these harsh man-made substances. In Pacific salmon, the common pesticide atrazine has been found to cause decreased gill function and migratory activity (Moore et al., 2008, p. 390). Other research shows that Pacific salmon populations are negatively affected both directly and indirectly by insecticides such as chlorpyrifos and carbaryl, which have been shown to alter the feeding behavior of Pacific salmon and decrease the salmon population through prey loss, respectively (Macneale et al., 2014). These examples only begin to illustrate a much larger problem, and that is the negative impact of pesticide runoff on aquatic ecosystems.

The United States has a global reputation for embodying the phrase “bigger is better”, and U.S. farming is no exception. Nearly 1.2 billion acres, which is over half the total acreage of the country, are devoted to agricultural purposes (United States Department of Agriculture, 2013)— and the industry is still growing, evidenced by US agricultural exports more than doubling between 2006 and 2013 (United States Department of Agriculture, 2014). With such a massive agricultural industry, any detrimental effects of modern farming practices have the potential to become equally immense. In fact, the largest cause of water quality impacts on river and lakes that were surveyed by the 2000 National Water Quality Inventory was agricultural nonpoint source pollution, or in laymen’s terms, pollution coming from multiple, diffused agricultural sources. Some activities that contribute to this nonpoint source pollution are the “improper, excessive, or poorly timed application of pesticides,” (Agricultural Nonpoint Source Fact Sheet, 2005).

Alternative Farming Practices

Although the problem is obvious, the solution is less clear. Alternative farming practices that reduce the use and runoff of pesticides are considered to be less economical than the conventional methods. Conventional farming, which includes the use of agricultural pesticides, produces higher crop yields than alternative methods such as organic farming (Brazinskiene, 2014). Another problem is that the prices of foods produced organically tend to be higher than the prices of foods that were produced under conventional farming methods (Morgan, 2000). A recent study has shown, however, that although the cost for producing organic crops is more, there are only negligible differences in the net return on the crops even without a premium being added to the price of the organic crops (Pimmental, Hepperly, Hanson, Douds, & Siedal, 2005)— this means that foods produced through alternative methods do not necessarily have to be more expensive for consumers in order to be economically viable.

In addition to organic farming as a means of decreasing the use of pesticides, implementing biological controls is an environmentally friendly farming practice. Biological control is the use of predator insects or natural enemies such as parasites and pathogens to manage the pest population to prevent damage that they cause to crops and farmland (University of California Agriculture & Natural Resources, 2014). Advantages to biological control include becoming a self-perpetuating system, not causing pollution to the environment, and not leaving residue on crops that pesticides would (Charlet, Olson, & Glogoza, 2002).

Crop rotation is another farming practice that helps to reduce the use of pesticides and provide substantial crop yields. According to George W. Roth of the Penn State College of Agricultural Sciences (1996), crop rotation can increase crop yields in comparison to traditional farming methods, decrease production cost, and be grown without the use of soil insecticides that contribute to pesticide pollution from runoff. Corn crops planted following soybeans can produce an increased yield of up to 20% as opposed to continuously planting corn (Roth, 1996). Crop rotation can benefit farmers economically as well. When switching from continuous crop growth to a crop rotation system, there is a decrease in input costs of $25 per acre if corn is planted following soybeans (Roth, 1996).

By switching to alternative methods of farming such as organic farming, biological pest control, and crop rotation, not only can farmers see a possible increase in crop yield, but the reduction of pesticide use from runoff will help improve the quality of water that affects not only human health but the health of aquatic ecosystems as well.

Pesticides and Aquatic Ecosystems

Aquatic ecosystems are highly complex environments that are extremely interconnected. Any small change made to an ecosystem, such as the availability of one food source or a shift in bacterial or phytoplankton diversity has the ability to affect multiple trophic levels. As aquatic food webs are extremely complicated, one small change can act as a disruptor to the equilibrium of the entire system (Dodds, Whiles, 2010).

Agricultural practices such as pesticides, antibiotics from fertilizers, and herbicides have serious environmental impacts in aquatic ecosystems. When considering these three stressors together we see changes via direct effects from antibiotics that result in bacterial population changes that affect the carbon cycle and can lead to anoxic conditions, we also see herbicides affecting the growth and diversity of photosynthetic species including primary producers, which affects the entire food chain in a ‘bottom-up’ capacity (Dodds, Whiles, 2010). Finally, we see pesticides directly affecting aquatic organisms through interference with normal biological mechanisms and also indirectly through prey-loss.

Pesticides in wetlands are highly dangerous stressors, as is the timing of pesticide exposure. Exposure during insect emergence period to which many aquatic predators are biologically synched to could be detrimental to fish and other species populations, the effect of which is likely to echo throughout the entire food web. These effects are especially important to consider for migratory species such as Atlantic and Pacific Salmon whose loss could affect both marine and freshwater ecosystems. A research paper by Moore et al. (2008) demonstrates the direct effects of the pesticide atrazine on Atlantic Salmon through decreased gill activity and reduced migratory activity, which can seriously affect population survival and recruitment.  In the research article, “A modeled comparison of direct and food web-mediated impacts of common pesticides on pacific salmon” (Macneale, Spromberg, Baldwin, & Scholz, 2014) argue that considering both the direct and indirect effects of insecticides is important to understanding their true impacts on Pacific Salmon populations. The paper showed both indirect and direct effects, directly through altered feeding behavior and indirectly by prey loss.


Implementing alternative farming practices such as crop rotation, organic farming, and biological pest control to reduce pesticide use and runoff from agricultural nonpoint source pollution will decrease its negative impact on water quality and aquatic life. By initiating programs such as the Hydrologic Unit Area and Demonstration Project programs, the United States Government has taken action to “provid[e] educational, technical, and financial assistance to support adoption of USDA Natural Resource Conservation Service (NRCS)-approved practices by farmers” (Osmond et al., 2012, p. 4). The initiation of governmental programs such as these show governmental support and acknowledgement of the issue that is water pollution.

Both the Hydrologic Unit Area and Demonstration Project programs were active from 1991 to 1994, implying that the issue of agricultural nonpoint source pollution has been an issue that has been recognized by the government for decades (Osmond et al., 2012). Water pollution from pesticide and waste runoff from farms has been an ongoing problem that affects not only aquatic ecosystems but our water supply as well.

According to the United States Environmental Protection Agency (2005), “agricultural nonpoint source (NPS) pollution is the leading source of water quality impacts on surveyed rivers and lakes, the second largest source of impairments to wetlands, and a major contributor to contamination of surveyed estuaries and groundwater” (Protecting Water Quality from Agricultural Runoff section, para. 2). The United States Environmental Protection Agency recognizes pollution from agricultural runoff as the main contributor to 70% of the pollution in streams and rivers as a result of current farming practices with irrigation systems that produce runoff of “chemicals, silt, and animal waste…U.S. farmland has polluted more than 173,000 miles of waterways” (Horrigan, Lawrence, & Walker, 2002, p. 447). These statistics are too large and impactful to ignore as a non-issue. Stricter government restriction of pesticide use and a push towards alternative farming practices needs to be implemented to reduce the rate of pesticide pollution that we are currently experiencing.

As a result of governmental pesticide restriction, the initial cost of production for the agricultural industry would increase, as would for consumers if switching to a less harmful pesticide (Buzby, Ready, & Skees, 1995). However, according to a case study on banning a post-harvest pesticide in grapefruit packing houses in Florida, the reduction in health risk from pesticide exposure outweighs the slight increase in produce cost (Buzby et al., 1995). By continuing the use of harmful pesticides, workers and consumers are at a greater risk for exposure. In this study, sodium ortho-phenylphenate is “a fungicide that reduces postharvest losses from blue molds, green molds, and stem end rots in grapefruit” (Buzby et al., 1995, p. 614). According to the authors, by banning sodium ortho-phenylphenate, the potential benefits could include improvements in “worker, environmental, and food safety” (p. 614). According to the Environmental Protection Agency, exposure to grapefruit treated with sodium ortho-phenylphenate has a cancer risk of 10 in 10,000, whereas switching to a less harmful but slightly more costly pesticide such as thiabendazole lowers that cancer risk to 10 in 10,000,000 (Buzby et al., 1994, p. 617). If the U.S. Government provides incentives to switch to a less harmful pesticide, this could be a good strategy to moves towards less impactful and toxic contamination from runoff, although changing farming practices to cut out pesticide use will provide better results as opposed to switching to less harmful pesticide use.

It is critical that pesticide use is regulated for the sake of the environment and human health. Clean water is imperative to avoid the ingestion and absorption of toxic chemicals that could result in long and short term health effects on the aquatic ecosystem and human health. Through governmental regulation and restriction of harmful pesticides by providing financial incentives for farmers, groundwater and freshwater contamination can be reduced and water pollution conditions improved.





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