Chemical Name: 2-chloro-4-(ethylamine)-6-(isopropylamine)-s-triazine
CAS: 1912-24-9, SMILES structure is ClC1=NC(NC(C)C) =NC(NCC)=N1
Atrazine is a s-triazine-ring herbicide that is used globally to stop pre and post emergence broadleaf and grassy weeds in major crops. Atrazine binds to the quinine-binding protein in photosystem II, inhibiting electron transport. Atrazine is one of the most widely used herbicides and according to the Environmental Protection Agency (EPA) the US used 363 million kg of Atrazine from 1980 to 1990. The herbicide is classified as a class C carcinogen which has been shown to cause chromosomal damage in hamster ovary cells. The half-life of atrazine in soil is 15 to 100 days. Alternative derivatives of atrazine as well as the breakdown products could be carcinogenic as well. Atrazine and its derivatives are used in many industrial processes as well, including use in dyes and explosives. Hydroxyatrazine is unregulated and no negative effect is known. Despite recommendations for controlled and managed atrazine applications, the use will probably continue to compromise soil and groundwater worldwide (Ralebitso TK, et al) (Wackett LP, et al).
The oral LD50 for atrazine is 3090 mg/kg in rats, 1750 mg/kg in mice, 750 mg/kg in rabbits, and 1000 mg/kg in hamsters. The dermal LD50 in rabbits is 7500 mg/kg and greater than 3000 mg/kg in rats. The 1-hour inhalation LC50 is greater than 0.7 mg/L in rats. The 4-hour inhalation LC50 is 5.2 mg/L in rats.
Atrazine is the most widely used pesticide in U.S. agriculture and is the predominant member of the triazine herbicide family.1 Although EPA restricts use to certified applicators, atrazine is used extensively in the Midwest, as well as in the Appalachian region, New England, and the Coastal Plains. Some 80 million pounds of atrazine are applied annually, primarily to corn, sorghum, and other crops. It is also registered for use on lawns and golf courses. Exposure occurs through inhalation, skin contact, or ingestion of contaminated food and water. Atrazine¡¯s extensive use, persistence in soil, and mobility in water make it the most frequently detected pesticide in ground and surface water across the U.S. Thus, drinking water is a common source of exposure, especially in agricultural regions. For example, testing has found atrazine in finished water from 97% of surface-water supplied drinking water systems in Iowa.In addition, a recent survey of nearly 1,500 groundwater wells around the country detected atrazine in 23% of the samples, and found it to be among the most common pollutants detected.
What Are The Health Effects of Atrazine in Drinking Water?
A growing body of toxicological and epidemiological evidence has raised concerns that chronic atrazine exposure may cause a variety of adverse human health effects. One epidemiological study found an association between maternal exposure to triazine herbicides in drinking water and increased incidence of developmental effects in newborns, including low birth weight.Reduced sperm counts, decreased sperm motility, and prostate inflammation have been observed in male laboratory rats exposed to atrazine.Endocrine disruption by atrazine and other triazine herbicides has also been reported in laboratory studies.Researchers have observed chromosomal damage in animal cell cultures exposed to atrazine at concentrations comparable to the federal drinking water standard.While animal studies have found that atrazine is carcinogenic at high doses administered orally, the evidence for cancer in humans is controversial. EPA classifies atrazine as ¡°not likely to be carcinogenic to humans.¡±However, the International Agency for Research on Cancer has concluded that atrazine is not classifiable as to its carcinogenicity in humans due to insufficient evidence.Human epidemiological studies on triazine herbicides have found associations with increased risk for breast cancer,ovarian cancer,and non-Hodgkin's lymphoma,although causality was not established. It is important to note that atrazine typically occurs in combination with other pesticides in drinking water, and the health effects of such mixtures are largely unknown.While the existing health effects data for atrazine are still sparse and in some cases inconclusive, the available evidence points to a need to minimize or prevent human exposures.
Is Atrazine of Greater Concern to Certain Populations?
Pesticides such as atrazine pose the greatest risk to the developing fetus, infants, and children. Developing biologicalsystems are more prone to chemical disruption, and immaturemetabolic systems are less able to detoxify pesticides.Children may be disproportionately exposed to atrazinebecause they drink more water than adults on a body weightbasis. Epidemiological and laboratory animal studies suggestthat prenatal and lactational exposure to atrazine can causeabnormalities in the developing fetus and newborn offspring,such as intrauterine growth retardation,low birth weight,and a higher rate of prostate inflammation in males.
What Can Health Professionals Do to Reduce the Public Health Threat from Atrazine?
In areas of high atrazine use (e.g., in ¡°cornbelt¡±communities in the Midwest), or if atrazine exposure issuspected, help patients to determine the source(s) of exposure. If drinking water is identified as a source of atrazine exposure, advise patients to switch to bottled water, or to use a home treatment unit. Because bottledwater can also contain contaminants, consumers should contact bottlers for testing results. Advise consumers toread labels on filtration units carefully to ensure that theyare effective for pesticide removal.
Encourage patients with private wells to have their water tested regularly for possible contamination. Local health departments can assist with testing.
Tell parents that infants who are fed formula reconstituted with contaminated tap water may be at significant risk from atrazine exposure, particularly in highly contaminated areas and during spring and summer. Pregnant or lactating women drinking tap water may also be at risk.
Advise patients to read the Consumer Confidence Reports provided by their local water utility. Utilities are required to provide these reports annually to bill-paying customers to identify contaminants that exceed federal standards.
Become involved in local, state, and national efforts to prevent atrazine contamination of drinking water. PSR's Safe Drinking Water Advocacy Kit includes advice on how to become involved
The start of atrazine biodegradation can occur by three known ways. Atrazine can be dechlorinated and then the other ring substituents are removed by amidohydrolases. These steps are performed by AtzA-C respectively, which are commonly produced by a single organism. The end product, cyanuric acid, is then used as a carbon and nitrogen source. The most characterized organism that performs this pathway is Pseudomonas sp. ADP. The other mechanism involves dealkylation of the amino groups. In this mechanism dechlorination can be performed in the second step to eventually yield cyanuric acid, or the end result is 2-chloro-4-hydroxy-6-amino-1,3,5-triazine, which currently has no known path to further degradation. This path can occur by a single Pseudomonas species or by a number of bacteria (Zeng Y, et al) (Wackett LP, et al).
Sorption of atrazine in soil determines the bioavailability to degradation, which is performed mostly by microbes. Low atrazine biodegradation rates are a product of low solubility and sorption to areas inaccessible by bacteria. The addition of surfactants increases the solubility, increasing catalysis. Before use the surfactant must be evaluated for its effect on the environment as well as its use as a preferential carbon and energy source must be evaluated. Atrazine itself is a poor energy source due to the highly oxidized carbons in the ring. It is catabolized as a carbon and nitrogen source in limiting environments although the optimum carbon and nitrogen availability is not known. It has been shown that inorganic nitrogen increases atrazine catabolism while organic nitrogen decreases it. Low concentrations of glucose can have the effect of decreasing bioavailability though formation of bound atrazine, while higher concentrations promote the catabolism of atrazine (Ralebitso TK, et al).
The genes AtzA-C have been found to be highly conserved in atrazine degrading organisms worldwide. This could be due to the mass transfer of AtzA-C on a global scale. In Pseudomonas sp. ADP, the atz genes are located non-contiguously on a plasmid with mercury catabolism genes as well. This plasmid is conjugatable to Gram negative bacteria in the lab and could easily lead to the worldwide distribution with the amount of atrazine and mercury being produced. AtzA-C have also been found in a Gram positive bacterium, but chromosomally located (Cai B, et al). This is not surprising due to the presence of insertion elements flanking each gene and the detection of these genes on different plasmids. Their configurations on these different plasmids suggest the insertion elements are involved in the assembly of this specialized catabolic pathway (Wackett LP, et al). Two options exist for degradation of atrazine using microbes: bioaugmentation or biostimulation (Wackett LP, et al)