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.
Synopsis by Dr. Ed Orlando and Wendy Hessler
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).
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 groups,
respectively.
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.
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.
Resources:
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.