Residues of atrazine and N-deethylated atrazine in water from five agricultural watersheds in Québec

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and N-deethylated atrazine (2-chloro-4-amino-6-isopropylamino-s-triazine) were monitored (1974 and 1975) in five rivers which drained agricultural areas in the Yamaska river basin of Québec. Water samples were collected frequently from April to December each year from sites near the outflow of each river. The water samples were extracted with benzene, chloroform, or ethyl acetate and the extracts were analyzed by gas chromatography using a Hall electrolytic conductivity detector and an alkali-flame detector. Atrazine and N-deethylated atrazine residues ranged in concentration from 0.01 to 26.6 microgram/L and less than 0.01 to 1.34 microgram/L, respectively, over the monitoring period. The highest levels of atrazine were observed in July each year and they coincided with the herbicide spraying season in this region and with occasional heavy rainfall events. Discharges (kg/yr) of atrazine from the five rivers were related to corn-growing area in each watershed. Losses of atrazine ranged from 0.1 to 2.9% of the atrazine that was estimated to have been applied in each watershed.     

Saliva biomonitoring of atrazine exposure among herbicide applicators

A field study was conducted in which saliva samples were collected from a cohort of herbicide applicators during the pre-emergent spray season in Ohio in 1996. Atrazine concentrations were detected in human saliva samples using an enzyme-linked immunosorbent assay (ELISA) method. Trend due to atrazine exposure and subsequent elimination in the body were evidenced by the temporal pattern of decreasing atrazine concentrations in saliva over time. Median salivary concentrations of atrazine on non-spray days were significantly lower than on spray days for each sampling time (Mann-Whitney U–Wilcoxon rank sum test, P < 0.01). Within spray days, median salivary atrazine concentrations were significantly higher on days atrazine was sprayed than on days herbicides other than atrazine were sprayed for each sampling time (Mann-Whitney U–Wilcoxon rank sum test, P=0.02 for 4–6 p.m. samples, P=0.04 for bedtime samples, P=0.03 for next-morning samples). Median salivary atrazine concentrations on days atrazine was sprayed were higher than the median concentration for the corresponding sampling time on non-spray days and on days when other herbicides were sprayed. Salivary concentration of atrazine is a plausible indicator of those days in which atrazine spraying was likely to have occurred. Salivary concentrations of atrazine not only reflect exposures resulting from spraying atrazine, but also exposures from other field activities where applicators may come in contact with atrazine. The results of this study confirmed data from animal experiments that atrazine is able to cross the cell membranes of salivary glands, and can be measured in human saliva with high sensitivity. The sampling method itself is convenient and easy to use in the field, with a high compliance rate, and analytical procedures are rapid and inexpensive. It is, therefore, concluded that saliva sampling of atrazine exposure among herbicide applicators is a feasible biomonitoring method. Received: 17 December 1999 / Accepted: 6 May 2000     

Perturbation of organogenesis by the herbicide atrazine in the amphibian Xenopus laevis

BACKGROUND: Exposure to anthropogenic chemicals during development can disrupt the morphogenesis of organ systems. Use of the herbicide atrazine has been debated in recent years because of its implicated, but poorly characterized, effects on vertebrates. Previous studies primarily examined the effects of atrazine exposure during metamorphosis or early developmental stages of amphibians. OBJECTIVES: We sought to identify and characterize the susceptibility during the often-overlooked developmental stage of organ morphogenesis. METHODS: We used a static renewal experimental treatment to investigate the effects of 10, 25, and 35 mg/L atrazine from early organ morphogenesis through the onset of tadpole feeding in the aquatic amphibian model system, Xenopus laevis. We quantified malformations of the body axis, heart, and intestine, as well as apoptosis in the midbrain and pronephric kidney. RESULTS: We found a significant dose-dependent increase in the percentage of atrazine-exposed tadpoles with malformations of multiple tissues including the main body axis, circulatory system, kidney, and digestive system. Incidence of apoptotic cells also increased in the both midbrain and kidney of atrazine-exposed tadpoles. CONCLUSIONS: Our results demonstrate that acute atrazine exposure (10-35 mg/L for < or = 48 hr) during early organ morphogenesis disrupts proper organ development in an amphibian model system. The concurrent atrazine-induced apoptosis in the pronephric kidney and midbrain begins to elucidate a mechanism by which atrazine may disrupt developmental processes in nontarget organisms.     

Mineralization of atrazine in agricultural soil: inhibition by nitrogen

Microbial mineralization of atrazine was characterized in soils and liquid media in the presence of nitrogen fertilizer concentrations representing typical field applications. The mineralization of atrazine in soils varied between 6 and 99% after 18 d of incubation. Half-lives of between 0.99 and more than 18 d were obtained. Mineralization kinetics and degree are related by a reciprocal trend to concentrations of available nitrogen in the soil. In liquid media, half-lives were calculated as 0.12 d in the absence of fertilizer nitrogen and as 79 d in the presence of 1,000 mg/L of KNO3-N. Only 20% of atrazine was mineralized after 18 d of incubation in the presence of this concentration of KNO3-N, whereas greater than 90% mineralization occurred after 2 d of incubation in liquid medium without KNO3-N. The results demonstrate that the mineralization of atrazine is inhibited even at fertilizer nitrogen levels lower than typical field applications. Inhibition in soil is lower than that in liquid medium, possibly because of the higher complexity of the soil system. This may explain why atrazine that infiltrates to the groundwater is persistent. The microbial consortium of the soils was characterized, and seven species were identified. The degrading capacity of these species suggests that only three species are involved in the degradation of atrazine.     

Cytogenetic studies of herbicide interactions in vitro and in vivo using atrazine and linuron

The herbicides atrazine and linuron, found in Wisconsin's groundwater, were tested alone and in combination, both in vivo and in vitro, to determine their individual and combined genotoxic effects. Human lymphocytes exposed in vitro to either 1 g/ml linuron or 0.001 g/ml atrazine showed little chromosome damage, whereas significant chromosome damage was observed in lymphocytes simultaneously exposed to 0.5 g/ml linuron and 0.0005 g/ml atrazine, suggesting at least an additive model. In another experiment, mice were fed 20 g/ml atrazine, 10 g/ml linuron, or a combination of 10 g/ml atrazine and 5 g/ml linuron in their drinking water for 90 days, after which bone marrow cells and cultured splenocytes were examined for chromosomal damage. None of the treatment groups showed chromosome damage in bone marrow, whereas the cultured splenocytes demonstrated damage in all treatment groups. These experiments suggest that, prior to assessing the risk of a herbicide, it may be necessary to test it in combinations which mimic the mixtures which would occur under field conditions, such as in contaminated groundwater.     

除草剂阿特拉津对中华大蟾蜍生存和性腺发育的影响

目的探讨三嗪类除草剂阿特拉津对本地种中华大蟾蜍生存和性腺发育的毒性。方法将中华大蟾蜍从发育的第27期开始暴露于不同质量浓度(0.1、1.0、10.0、100.0μg/L)的阿特拉津,直到变态结束(3个月)后将其解剖,取性腺做组织学观察。暴露期间,每天记录蝌蚪的生长发育情况和死亡情况。结果实验组按质量浓度梯度由小到大,100.0μg/L暴露组死亡率与对照组比较,差异有统计学意义(P<0.05);虽然各组之间差异无统计学意义,但是阿特拉津在一定程度上干扰了中华大蟾蜍的生长发育;阿特拉津导致暴露组均出现不变态的蝌蚪;阿特拉津对中华大蟾蜍卵巢组织学没有明显影响;却导致雄性性腺发育迟缓,并在一定程度上导致了睾丸组织结构的改变。结论阿特拉津可能通过雌性化/去雄性化作用影响中华大蟾蜍睾丸的发育,有待分子水平的进一步研究。     

Effects of the herbicide atrazine and its degradation products,alone and in combination,on phototrophic microorganisms

Toxic effects of the herbicide atrazine and four of its degradation products were determined for growth, photosynthesis, and acetylene-reducing ability of two species of green algae and three species of cyanobacteria. Atrazine was significantly more toxic than its degradation products towards the above test criteria, yielding EC₅₀ values ranging from 0.1 to 0.5 ppm (g/ml) for photosynthesis and 0.03 to 5.0 ppm for growth. Deethylated atrazine was the next most toxic with EC₅₀ values of 0.7 to 4.8, and 1.0 to 8.5 ppm for photosynthesis and growth, respectively. With deisopropylated atrazine the EC₅₀ values for the same physiological functions ranged from 3.6 to 9.3, and 2.5 to >10 ppm, respectively. Hydroxy- and diamino-atrazine were non-toxic towards most of the cultures tested. Acetylene reduction with cyanobacteria was found to be insensitive to all of the test compounds, except for atrazine, which had an EC₅₀ of 55 ± 15 ppm towardsAnabaena inaequalis. Combinations of atrazine and its monodealkylated products were tested withA. inaequalis and yielded both synergistic, antagonistic, and additive interaction responses, depending upon the actual test system employed.     

Sequential bio- and phototransformation of the herbicide methabenzthiazuron in water

We investigated the transformation of methabenzthiazuron in water by microorganisms and solar light. This compound was very slowly phototransformed when irradiated at lambda > 290 nm, but it could be successfully oxidized into 6-hydroxymethabenzthiazuron by Aspergillus niger, as shown by nuclear magnetic resonance experiments. The toxicity of this metabolite, as determined by the standardized Microtox test, was sixfold lower than that of the parent molecule. The 6-hydroxymethabenzthiazuron was not further metabolized by A. niger but was photooxidized with ring cleavage of the aromatic ring and photodimerized on irradiation at lambda > 290 nm. In the presence of humic substances, the photodegradation was slower. We demonstrate that the transformations of methabenzthiazuron, observed either with the fungus A. niger or by the action of solar light, do not proceed via the urea chain N-dealkylation, as usually reported, but only via hydroxylation or cleavage of the benzene ring. This work shows the complementarity of both approaches, photo- and biodegradation, to study the fate of herbicides in the environment.     

In situ water and sediment toxicity in an agricultural watershed

The Salinas River receives inputs from extensive farmlands before flowing into the Salinas River National Wildlife Refuge and the Monterey Bay National Marine Sanctuary (CA, USA). Previous monitoring using laboratory toxicity tests and chemical analyses identified toxic agricultural drain-water inputs in this system. Using caged daphnids (Ceriodaphnia dubia) and amphipods (Hyalella azteca), we investigated in situ toxicity at stations downstream from an agricultural drain relative to a reference station. A flow sensor indicated highly variable inputs from irrigation, and daily synoptic chemical analyses using enzyme-linked immunosorbent assay techniques demonstrated fluctuating concentrations of organophosphate pesticides. Test organism mortality in the field coincided with contaminant concentrations that exceeded chemical effect thresholds for the test species. Laboratory toxicity tests using C. dubia were comparable to results from field exposures, but tests with H. azteca were not. Laboratory exposures can be reasonable surrogates for field evaluations in this system, but they were less effective for assessing short-term temporal variability. Results from the field toxicity studies corroborated results of bioassessment surveys conducted as part of a concurrent study. Toxicity identification evaluations indicated that organophosphate pesticides caused toxicity to daphnids and that effects of suspended solids were negligible.