Quantification of Changes in Chemical Pesticide Human Health Risk Following the Introduction of Bt Cotton and Herbicide-tolerant Soybean: A Case Study

ABSTRACT

Human health risks associated with changes in synthetic chemical pesticide use following the introduction of genetically modified crops are quantified in this article. Bacillus thuringiensis ( Bt ) cotton and herbicide-tolerant (HT) soybean, two genetically modified crops, were chosen as the focus for this study based on their global popularity. An innovative multimedia total exposure model, CalTOX, was used to calculate the health risks for two target populations, before and after the introduction of Bt cotton and HT soybean. Major results include the quantification of incremental lifetime cancer risk based on a time-weighted average exposure, and the quantification of hazard ratios for non-cancer effects based on the maximum exposure rate value, both computed over the exposure duration. Results show that human health risks are not intuitively and necessarily reduced with the reduction of pesticide use. For example, more trifluralin was used after the introduction of HT soybeans in Iowa and Minnesota, leading to higher risks. Moreover, the general population may have larger exposures to pesticides when compared with the population living in areas where pesticides are actually applied. This may occur because exposure to pesticides is not only dependent on geographical distance from the contaminated area, but also strongly dependent on other factors, such as the characteristic travel distance and environmental persistence.

Keywords:

• genetically modified crops
• insecticides
• Bt cotton
• HT soybean
• human health risk
• exposures

Notes

¹The USEPA has determined the potential for some of these products to cause cancer. Group C: Possible human carcinogen. Limited evidence of carcinogenicity in animals in the absence of human data. Group E: Evidence of non-carcinogenicity for humans. No evidence of carcinogenicity in at least two adequate animal tests in different species or in both adequate epidemiologic and animal studies. The USEPA uses the oral LD50, inhalation LC50, dermal LD50, eye effects, and skin effects, to rank pesticides into four toxicity categories. The most acutely toxic pesticides are in Category I and the least toxic in Category IV. These criteria are based on the results of animal tests done in support of registration of the pesticide.

^a USEPA (1989);

^b USGS (2004).