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The process of bioaccumulation starts when pesticides applied to agricultural land runoff during storms into rivers, streams and eventually the ocean. The pesticides become part of the water column and fish ingest the pesticides, usually through their gills, although sometimes through their fish scales. The pesticides go into their organs and fat tissue and are sequestered there. More and more pesticides are ingested and stored in organs and tissues as fish get oxygen from the water column for survival. These accumulated pesticides accumulate up the food chain as big fish eat little fish and eventually as humans eat the fish.
Bioaccumulation is affected by how much of the pollutant gets into each organism; the effectiveness of the elimination process of each organism; organism metabolic process; organism fat content; and the solubility of the pollutant. To get an accurate picture of threats to humans, this type of information for each organism within the food chain must be obtained and added. The EPA has identified tolerance levels for pollutants. Bioaccumulation values help determine tolerance levels in which no harm to human health will take place. Fish advisories for pregnant woman and children are more stringent because they have different metabolic processes occurring; the same stringency applies to people with serious illnesses.
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Pesticides are applied to get rid of pests. There are hundreds of types of pesticides. Some, like DDT used to eradicate malaria carrying mosquitoes, are banned for use in the United States because of their harmful ecological effects. The EPA provides strict guidelines on pesticide use to protect people applying the pesticide and also to prevent excessive amounts from impacting the environment. However, pesticide application to increase crop yields ends up washing off through irrigation and precipitation events entering waterways which are habitats for fish.
Pesticides that are water soluble are the most likely to bioaccumulate in fish. Omega - 3s offer excellent health benefits but they come from the fatty tissues of fish which are also the best part of the fish to store pesticides. Problems occur when people who want to improve their health naturally, rely on omega-3s, but unknowingly ingest high amounts of pesticides.
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Human Health Effects
Pesticides ingested and bioaccumulated through eating fish or taking omega-3 supplements can cause significant health problems. Organochlorines, a group of pesticides in which DDT belongs, are known as endocrine disrupters because they disrupt normal hormone processes which are the driving force behind every biological process. Organochlorines, even at very low concentrations, interfere with reproduction, growth and development. For this reason, there are many federal agencies that study and regulate pesticides including the EPA, Food and Drug Administration (FDA) and National Institutes of Health.
The FDA produces a total diet study that evaluates the pesticide residues found in fish, meats, dairy, fruits and vegetables as prepared (cooked) in an average US diet. In 2007, 15.6% of the total fish and shellfish sample, contained pesticide residues but no fish or shellfish had levels in violation of federal standards set to protect human health. The total diet study showed that bioaccumulation of pesticides in cooked fish is not problematic to adults eating an average US diet, as long as no serious health issues are apparent.
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FDA-The Total Diet Study
National Institutes of Health - Effects of Organochlorine
Pesticides - US EPA