CAS No. 1912-24-9
Atrazine is a widely used chlorotriazine herbicide active against broadleaf and grassy weeds. Related chlorotriazine herbicides include simazine, propazine, and cyanazine, all which act by inhibiting plant photosynthesis. Atrazine is applied pre- and post-emergence to agricultural land for crops such as corn and sorghum. It is also used as a non-selective herbicide. Atrazine was first registered as an herbicide in 1958. More than 70 million pounds have been applied annually in recent years, with about 75% of corn cropland receiving treatment. Atrazine has limited water solubility and is not tightly bound to soil, but is leachable in to ground and surface waters. In regions where atrazine is used, it is one of the more commonly detected pesticides in surface and ground waters (USGS, 2007). In soils, atrazine is slowly degraded to dealkylated products, which have half-lives of several months. Bacteria and plants can metabolize atrazine to hydroxyatrazine. Atrazine does not bioaccumulate. It has little toxicity in birds and moderate toxicity in some fish and aquatic invertebrates. Atrazine may alter the sexual development of frogs at environmental levels (Gammon et al., 2005; Hayes et al., 2002; U.S.EPA, 2003a).
For the general population, drinking water is an infrequent source of atrazine exposure, but estimates of seasonal intakes from drinking water in a small number of communities have exceeded the recommended limits (U.S.EPA, 2003b). As a result, atrazine use has progressively been restricted in an effort to reduce surface and ground water contamination. Applicators of atrazine may be exposed dermally and by inhalation. Atrazine is well absorbed orally, metabolized, and then eliminated in the urine over a few days (Bradway et al., 1982; Catenacci et al., 1993; Timchalk et al, 1990). In animals and humans, glutathione conjugation appeared to be the major route of biotransformation, resulting in atrazine mercapturate and N-dealkylation (IPCS, 1996; U.S.EPA, 2003b). Atrazine mercapturate accounted for a major proportion of human urinary metabolites (Lucas et al., 1993). The dealkylated chloroatrazine metabolites, particularly diaminochloroatrazine (the main dealkylated product), may mediate some effects of atrazine (Laws et al., 2003). Dealkylated metabolites from atrazine can result also result from metabolism of other chlorotriazine pesticides, including simazine, propazine, and cyanazine. In addition being human metabolites of atrazine, the dealkylated atrazine metabolites and hydroxyatrazine can occur in the environment from the breakdown of the parent chemical. Thus, detection of these dealkylated metabolites in a person's urine may also reflect exposure to these degradates in the environment.
Human health effects of atrazine at environmental doses or at biomonitored levels from environmental exposure are unknown. In mammalian studies, atrazine is rated as having low acute toxicity. Atrazine product formulations can be mild skin sensitizers and irritants. Chronic high dose toxicity observed in animals have demonstrated decreased body weight, myocardial muscle degeneration, liver toxicity, developmental ossification defects, impaired fertility, altered estrus cycles, increased pituitary weight, delayed onset of puberty, and reduced levels of luteinizing hormone, prolactin, and testosterone (Gillis et al., 1994; Laws et al., 2000 and 2003; Rayner et al., 2004; Stoker et al., 2000 and 2002; U.S.EPA, 2003b). Atrazine and the dealkylated chlorinated metabolites did not have estrogen receptor activity, but reduced the pituitary secretion of luteinizing hormone and prolactin and also inhibited aromatase at high doses in some mammalian species (Cooper et al., 2000; Eldridge et al., 1994 and 1999; Gammon et al., 2005; Sanderson et al., 2002; Stevens et al., 1999). Estimated human exposures are thousands of times lower than doses that caused effects in animals (Gammon et al., 2005). Some human ecologic and epidemiologic studies of reproductive and cancer outcomes have shown either positive or no associations, but are effects are difficult to attribute due to lack of exposure markers or due to mixed chemical or pesticide exposures (ATSDR, 2003; Gammon et al., 2005; Sathiakumar and Delzell, 1997). Atrazine is not considered genotoxic. IARC considers atrazine not classifiable with respect to human carcinogenicity, and U.S.EPA considers atrazine unlikely to be a human carcinogen. Additional information is available from U.S. EPA at: http://www.epa.gov/pesticides/ and from ATSDR at: http://www.atsdr.cdc.gov/toxprofiles/index.asp.
Urinary levels of atrazine mercapturate reflect recent exposure. In the NHANES 1999-2002 subsamples, levels of atrazine mercapturate were generally not detectable (CDC, 2009). In small studies of Maryland residents in 1995-1996 (MacIntosh et al., 1999) and 83 Minnesota children with multiple urine collections during 1997 (Adgate et al., 2001), atrazine mercapturate was infrequently detected at the detection limit of < 1 µg/L. In a study of 60 farm worker children, atrazine was detected in only four children (Arcury et al., 2007). Using immunoassay atrazine equivalents (detected mostly as atrazine mercapturate), the urinary geometric mean levels for herbicide applicators in Ohio and Wisconsin were about 6 µg/L (Hines et al., 2003; Perry et al., 2000). The geometric mean of urinary atrazine mercapturate was 1.2 µg/L in 15 farmers studied several days after spraying the pesticide (Curwin et al., 2005). In a small number of field workers, urinary concentrations ranged from 5-1756 µg/L (Lucas et al., 1993).
Finding measurable amounts of atrazine mercapturate in urine does not imply that the levels of atrazine mercapturate cause an adverse health effect. Biomonitoring studies on levels of atrazine mercapturate provide physicians and public health officials with reference values so that they can determine whether people have been exposed to higher levels of atrazine than are found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.
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