How a polluted environment can lead to illness
A study published Monday in the journal Pediatrics revealed alarming findings: A link between children diagnosed with Attention Deficit/Hyperactivity Disorder (ADHD) and traces of the breakdown of organophosphate pesticides in their urine. Specifically, the higher the concentration of metabolized pesticides like dimethyl alkylphosphate the researchers found in a participant’s urine, the more likely he or she met the criteria for an ADHD diagnosis. According to a post from Discover website’s 80beats blog:
[T]here are about 40 organophosphate pesticides in use in the United States, the most famous of which is malathion. It was heavily sprayed in California in the early 1980s to try to kill the Mediterranean fruit fly and also about a decade ago to try to stop the spread of West Nile virus.
Chemical applications in agriculture are considered commonplace, and as a result, humans and wildlife can be exposed to toxins through food and water contamination. A study in the March issue of Toxicology and Industrial Health, for example, linked herbicides and Parkinson’s disease. However, this is just one example of ways in which pollutants can impact human lives: Think of standing behind a truck’s exhaust pipe or the ominous Gulf oil slick that is currently creeping toward Florida.
Studies have shown that pollutants can have both direct and indirect effects on human and wildlife health as a result of changes in an ecosystem. Consumption of pesticide- and herbicide-tainted foods and carbon monoxide inhalation from car exhaust are examples of firsthand exposure; so is drinking water contaminated by rocket fuel in California or by mountaintop mining runoff in West Virginia.
Mountaintop mining, in particular, has shown to have a continuous effect on the health of West Virginia, Kentucky and Virginia residents. A study published in the January 8 edition of Science, for instance, revealed the many ways in which this mining practice—blasting off the top of a mountain to expose coal seams and depositing the debris in nearby valleys and streams (so-called “valley fills”)—can be directly detrimental to the local environment and to the health of West Virginia residents and wildlife:
Water emerges from the base of valley fills containing a variety of solutes toxic or damaging to biota. Declines in stream biodiversity have been linked to the level of mining disturbances in WV watersheds. Below valley fills in the central Appalachians, streams are characterized by increases in pH, electrical conductivity and total dissolved solids due to elevated concentrations of sulfate, calcium, magnesium and bicarbonate ions.
Changes in stream ecosystems caused deformities in larval fish, increased selenium exposure—thus contributing to reproductive failure—in adult fish and exposed birds to toxic selenium levels as they ate contaminated fish, said the study’s author Margaret Palmer from the University of Maryland and colleagues. Mine runoff also contributed to eutrophication and the microbial production of hydrogen sulfide, a toxin in aquatic ecosystems. Elevated selenium levels in streambed algae—which can have bioconcentrations as high as 800 to 2000 times more than water concentrations—also increased the chances of poisoning fish and other wildlife, they said.
As for the effect on West Virginians, the researchers found that direct exposure to toxins in streams or through ingesting polluted well water or selenium-contaminated fish can lead to illness. Dust particles and airborne toxins from the mine sites also were linked to pulmonary and other diseases. The authors wrote:
Adult hospitalizations for chronic pulmonary disorders and hypertension are elevated as a function of county-level coal production, as are rates of mortality, lung cancer and chronic heart, lung and kidney disease.
Another study published last month in EcoHealth tied the ecological integrity of West Virginia streams near mining sites to area residents’ cancer mortality rates. Nathaniel Hitt from Virginia Tech and Michael Hendryx from West Virginia University found that concentrations of residents with cancer increased in areas of high mining intensity. In addition, they discovered that as the ecological integrity of an area diminished, cancer mortality rates increased. As they wrote in the study:
Cancer types exhibited distinct relations to ecological integrity. Digestive, breast, respiratory, and urinary cancer mortality rates were significantly correlated [with ecological integrity], whereas mortalities from female or male genital cancer, oral cancer and ‘other’ cancers were not. Regression models revealed that poverty, smoking and urbanization were significant predictors of total cancer mortality but did not account for the observed relation between ecological integrity and cancer mortality.
Although the introduction of toxins to aquatic ecosystems is an example of a direct impact from pollution, nutrient enrichment, on the other hand, can indirectly affect human and wildlife health as well. For example, harmful algal blooms—the spread of which are amplified by nutrient enrichment in aquatic ecosystems, leading to a boost in algae and cyanobacteria—are toxic to humans and wildlife if ingested. They also grow rapidly, forcing other organisms to compete for dissolved oxygen in the water.
In addition, nutrient enrichment has been shown to increase incidents of malaria and other mosquito-borne illnesses. According to a study published in the January edition of Ecological Applications, abundant vegetation cover from nutrient enrichment in lakes, for instance, would protect mosquitoes from fish hunting for bugs at the water’s surface. As a result, populations of mosquitoes and of the malaria-causing protist, Plasmodium, are able to increase. As mentioned in a previous EcoTone post, West Nile virus was shown to be more prevalent with nutrient enrichment:
[F]emale Culex restuans mosquitoes, which are known for transmitting West Nile virus, oviposited more than ten times the number of egg clutches in containers with elevated nutrient levels than in containers with normal levels.
Scientists are still unraveling the complex ways—seen and unseen—in which public health is connected to ecosystem health. But one thing can be said: Pollution is prevalent in the United States and globally, and it is likely a significant factor in human and wildlife health.
Bouchard, M., Bellinger, D., Wright, R., & Weisskopf, M. (2010). Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides PEDIATRICS DOI: 10.1542/peds.2009-3058
Palmer, M., Bernhardt, E., Schlesinger, W., Eshleman, K., Foufoula-Georgiou, E., Hendryx, M., Lemly, A., Likens, G., Loucks, O., Power, M., White, P., & Wilcock, P. (2010). Mountaintop Mining Consequences Science, 327 (5962), 148-149 DOI: 10.1126/science.1180543
Hitt NP, & Hendryx M (2010). Ecological Integrity of Streams Related to Human Cancer Mortality Rates. EcoHealth PMID: 20361230
Johnson, P., Townsend, A., Cleveland, C., Glibert, P., Howarth, R., McKenzie, V., Rejmankova, E., & Ward, M. (2010). Linking environmental nutrient enrichment and disease emergence in humans and wildlife Ecological Applications, 20 (1), 16-29 DOI: 10.1890/08-0633.1