New research by scientists at the Centers for Disease Control indicates that the analysis the CDC has used to estimate human exposure to atrazine and atrazine-related breakdown products has strongly underestimated its extent.
Barr, D, B Panuwet, P Nguyen, JV Udunka, S and LL Needham. 2007. Assessing exposure to atrazine and its metabolites using biomonitoring. Environmental Health Perspectives 115:1474–1478.
New research by scientists at the Centers for Disease Control indicates that the analysis the CDC has used to estimate human exposure to atrazine and atrazine-related breakdown products has strongly underestimated its extent. The CDC has depended upon detecting one atrazine metabolite, atrazine mercapturate. By looking for other metabolites, CDC scientists have found that the old method misses most of the exposure.
What did they do?
Barr et al. measured nine different atrazine metabolites in urine samples from 24 people using high performance liquid chromatography and tandem mass spectrometry (HPLC-MSMS). The people sampled differed with respect to how likely they were to be exposed to atrazine: high exposure (turf pesticide applicators), low exposure (non-occupationally exposed people in whom atrazine mercapturate was found during a prior study) and environmental exposure (volunteers with no known exposure to atrazine).
What did they find?
Urinary metabolite concentrations varied dramatically among atrazine exposure categories and between individuals in a single category. Diaminochlorotriazine (DACT) was the most commonly measured metabolite, contributing 51% of atrazine-related metabolites in turf applicators, 28% to the low exposure group and 77% to the environmental exposure group (graphs below). In contrast, atrazine mercapturate (AM) contributed only 12%, 6% and 2% to samples from those
The variation in the proportion of total atrazine metabolites among samples was consistently large, suggesting that one metabolite alone could not be used to determine true atrazine exposure in humans.
The graphs above compare estimates of atrazine-related exposures using only atrazine mercapturate (left) to estimates using 7 metabolites, including AM, for 8 turf applicators. Applicator #8 appeared to have the highest atrazine exposure using the AM estimate, but when 7 metabolites were measured, #2 emerged as most exposed.
What does it mean?
These data show that the CDC has systematically and strongly underestimated American exposure to atrazine and its metabolites. Previous research, which has relied upon atrazine mercapturate, gives a low and misleading estimate of exposure to atrazine and atrazine-related metabolites. Previous surveys by the CDC, measuring AM, had suggested that fewer than 5% of people carry measurable traces of atrazine, despite how commonly it is used and how frequently it is found in drinking water. It is clear that most, if not all, of the atrazine metabolites will need to be measured in order to get the most accurate picture of atrazine exposure.
Detection in urine of atrazine itself, or the metabolite atrazine mercapturate, is definitive evidence of direct exposure to atrazine. The other metabolites, however, are also formed via environmental degradation and are detected in water and can even be bound in the tissue of plants. Hence their presence in urine may indicate indirect exposure to atrazine-related metabolites. This is likely to be the reason why AM is much more common in turf applicators than in the other exposure groups.
The results of this study are important but are based on a small sample size. To further refine assessments of atrazine exposure, it will be important to examine other atrazine metabolites not measured in this research.
Atrazine is the second most commonly used herbicide in the United States. It is widely applied in the US mid-west to control weeds in field crops, especially corn and sorghum. It is also used on golf courses and sod farms for weed control.
The European Union banned atrazine in 2003 based on health concerns (Sass and Colangelo 2006), including tumors and endocrine changes. Exposure to atrazine is implicated in the altered gonadal development resulting in the formation of ovarian tissue in male frog gonads (Hayes et al. 2006). In vitro studies show that atrazine induces aromatase gene expression and activation of the aromatase enzyme (Sanderson et al. 2000). Other studies indicate that atrazine is correlated with tumor formation and suggest that atrazine alters the regulation of steroid hormone synthesis by changing how the brain and pituitary control the gonad (Cooper et al. 2007).
Human exposure to atrazine is considered harmful at levels higher than 3 parts per billion (the Maximum Contaminant Level), according to the US Environmental Protection Agency. Exposure to higher amounts is associated with cardiovascular problems, adrenal gland damage, muscle spasms, retinal damage and cancer. Mostly, people are exposed to the herbicide through drinking water.
While research has identified at least 12 different metabolites that are formed as atrazine degrades, CDC research estimating the extent of human exposure has measured just one, atrazine mercapturate (AM). AM is detected in fewer than 5% of samples from the NHANES survey, indicating limited exposure. This observation was puzzling in light of how widespread use of atrazine is and how frequently it is detected in drinking water.
- Cooper RL, SC Laws, PC Das, MG Narotsky, JM Goldman, EL Tyrey, et al. 2007. Atrazine and reproductive function: mode and mechanism of action studies. Birth Defects Research Part B, Developmental and Reproductive Toxicology 80: 98-112.
Hayes TB, AA Stuart, M Mendoza, A Collins, N Noriega, A Vonk, et al. 2006. Characterization of atrazine-induced gonadal malformations in African clawed frogs (Xenopus laevis) and comparisons with effects of an androgen antagonist (cyproterone acetate) and exogenous Estrogen (17-beta-estradiol): Support for the demasculinization/feminization hypothesis. Environmental Health Perspectives 114(S1):134-141.
Sanderson JT, W Seinen, JP Geisey, M van den Berg. 2000. 2-Chloro-s-triazine herbicides induce aromatase (CYP19) activity in H295R human adrenocortical carcinoma cells: a novel mechanism for estrogenicity? Toxicological Sciences 54(1):121-127.
Sass JB and A Colangelo. 2006. European Union bans atrazine, while the United States negotiates continued use. International Journal of Occupational and Environmental Health 12(3):260-267 [PDF].
US Environmental Protection Agency. Atrazine fact sheet.