Study of pesticide genotoxicity

Evaluation of Genotoxic and Mutagenic Activity of Organic Extracts from Drinking Water Sources

An increasing number of industrial, agricultural and commercial chemicals in the aquatic environment lead to various deleterious effects on organisms, which is becoming a serious global health concern. In this study, the Ames test and SOS/umu test were conducted to investigate the potential genotoxicity and mutagenicity caused by organic extracts from drinking water sources. Organic content of source water was extracted with XAD-2 resin column and organic solvents. Four doses of the extract equivalent to 0.25, 0.5, 1 and 2L of source water were tested for toxicity. All the water samples were collected from six different locations in Guangdong province. The results of the Ames test and SOS/umu test showed that all the organic extracts from the water samples could induce different levels of DNA damage and mutagenic potentials at the dose of 2 L in the absence of S9 mix, which demonstrated the existence of genotoxicity and mutagenicity. Additionally, we found that Salmonella typhimurium strain TA98 was more sensitive for the mutagen. Correlation analysis between genotoxicity, Organochlorine Pesticides (OCPs) and Polycyclic Aromatic Hydrocarbons (PAHs) showed that most individual OCPs were frame shift toxicants in drinking water sources, and there was no correlation with total OCPs and PAHs.

Evaluation of the cytogenetic damage induced by the organophosphorous insecticide acephate

The organophosphorous insecticide acephate was tested for its ability to induce in vitro cytogenetic effect in human peripheral lymphocytes by using the chromosomal aberrations (CAs), sister chromatid exchange (SCE) and micronuclei (MN) assay. The level of nuclear DNA damage of acephate was evaluated by using the comet assay. Concentrations of 12.5, 25, 50, 100 and 200 mug mL(-1) of acephate were used. All concentrations of acephate induced significant increase in the frequency of CAs and in the formation of MN dose dependently (r = 0.92 at 24 h, r = 0.95 at 48 h for CAs, r = 0.87 for MN). A significant increase was observed in induction of SCE at 50, 100 and 200 mug mL(-1) concentrations during 24 h treatment and at all concentrations (except 12.5 mug mL(-1)) during 48 h treatment period in a dose-dependent manner (r = 0.84 at 24 h, r = 0.88 at 48 h). Acephate did not affect the replicative index and cytokinesis-block proliferation index (CBPI). However, it significantly decreased the mitotic index at all three highest concentrations (50, 100, 200 mug mL(-1)) for 24 h treatment and at all concentrations (except 12.5 mug mL(-1)) for 48 h treatment, dose-dependently (r = 0.94 at 24 h, r = 0.92 at 48 h). A significant increase in mean comet tail length was observed at 100 and 200 mug mL(-1) concentrations compared with negative control in a concentration-dependent manner (r = 0.94). The mean comet tail intensity was significantly increased at only 200 mug mL(-1) concentration. The present results indicate that acephate is a clastogenic, cytotoxic agent and it causes DNA damage at high concentrations in human lymphocytes in culture.

In vivo genotoxicity of atrazine to anuran larvae

Atrazine has been an environmental contaminant for more than two decades. While there can be little dispute as to the presence of atrazine in non-target watersheds, the debate has centered on the consequences of this contamination. The purpose of this study was to determine if atrazine is genotoxic to developing anurans. Anurans are one of the groups that have the highest potential for being affected by watershed contamination. In initial studies, larvae from two anuran species were exposed to known genotoxic agents. Upon flow cytometric analysis, those organisms exposed to the genotoxic agents resulted in a statistically significant increase in nuclear heterogeneity. Having demonstrated that flow cytometric analysis could be used to detect genotoxicity in anuran larvae, the larvae of the two species were exposed to different levels of atrazine for various durations. The concentrations and lengths of exposure were consistent (albeit on the higher side) with conditions found in the Midwestern US. In neither species was an increase in nuclear heterogeneity observed. Thus, atrazine at levels and time of exposure representing conditions found contaminating Midwestern watersheds does not appear to be genotoxic to developing anurans.

Evaluation of genotoxicity of captan, maneb and zineb in the wing spot test of Drosophila melanogaster: role of nitrosation

The wing spot test in Drosophila melanogaster is a suitable system for the analysis of genotoxic activity of compounds that need metabolic transformation to render them active. We have analysed the genotoxicity of three fungicides for which it was reported that the metabolic processes taking place in vivo may determine their activity. The compounds analysed are captan, maneb, zineb and ethylenethiourea (ETU) (a metabolic derivative of ethylenebisdithiocarbamates like maneb and zineb). We have also evaluated the ability of ETU to form genotoxic derivatives in vivo analysing this compound in combined treatments with sodium nitrite. Both standard and high bioactivation NORR strains have been used. Captan, usually considered a mutagen in vitro but a non-mutagen in vivo, gave negative results in the wing spot test with both crosses. Positive results were obtained for maneb in the standard cross and for ETU in both the standard and the high bioactivation cross. The genotoxicities of maneb and ETU were higher when treatments were made on media in which nitrosation is favoured. A low absorption of the fungicide and an inefficient availability of the compound in the target may explain negative results obtained with zineb in both crosses. The results obtained in this study with the wing spot test demonstrate once again the suitability of this in vivo assay, in which absorption, distribution and metabolism processes take place, for the evaluation of genotoxicity of compounds to which humans are exposed.

Assessment of genotoxic effects of chloropyriphos and acephate by the comet assay in mice leucocytes

Two organophosphorus (OP) pesticides (chloropyriphos and acephate) and cyclophosphamide (CP) (positive control) were tested for their ability to induce in vivo genotoxic effect in leucocytes of Swiss albino mice using the single cell gel electrophoresis assay or comet assay. The mice were administered orally with doses ranging from 0.28 to 8.96 mg/kg body weight (b. wt.) of chloropyriphos and 12.25 to 392.00 mg/kg b.wt. of acephate. The assay was performed on whole blood at 24, 48, 72 and 96 h. A significant increase in mean comet tail length indicating DNA damage was observed at 24h post-treatment (P<0.05) with both pesticides in comparison to control. The damage was dose related. The mean comet tail length revealed a clear dose dependent increase. From 48 h post-treatment, a gradual decrease in mean tail length was noted. By 96 h of post-treatment the mean comet tail length reached control levels indicating repair of the damaged DNA. From the study it can be concluded that the comet assay is a sensitive assay for the detection of genotoxicity caused by pesticides.

Genotoxic effects of malathion: an organophosphorus insecticide, using three mammalian bioassays in vivo

The genotoxic effects of malathion was evaluated using chromosome aberration, sister chromatid exchange (SCE) and sperm abnormality assays in mice. All the three acute doses (2.5, 5 and 10mg/kg) of malathion tested in the present study, induced significant dose-dependent increase in the frequency of chromosome aberrations and sperm abnormalities, but did not affect the total sperm count. The highest acute dose induced a >12-fold increase in the frequency of chromosome aberrations, two-fold increase in the frequency of SCEs and four-fold increase in the frequency of sperms with abnormal head morphology following intraperitoneal (i.p.) exposure. Further, a significant increase in the frequency of SCEs was observed, but the increase was not dose-dependent. At higher doses, malathion induced a moderate delay in cell cycle as evident from the increase in average generation time (AGT). The present findings suggest that technical grade malathion is a potent genotoxic agent and may be regarded as a potential germ cell mutagen also.

Detection of DNA damage in mouse peripheral blood leukocytes by the comet assay after oral administration of monocrotophos

The objective of this study was to determine if single/double strand DNA breaks could be induced by monocrotophos (organophosphorus pesticide) in mice in vivo using the comet assay. Mice were dosed orally with 0.046, 0.093, 0.186, 0.373 and 0.746 mg/kg body weight of monocrotophos, and the assay was performed on whole blood after 24, 48 and 72 h. A significant increase in mean comet tail length indicating DNA damage was observed at 24 and 48 h post-treatment with monocrotophos when compared to controls. A decrease in the mean tail length was observed at 72 h post-treatment indicating repair of the damaged DNA. The mean tail length showed a dose-related increase and time dependent decrease. The study reveals that comet assay is a sensitive and rapid method to detect genotoxicity of monocrotophos.

Evaluation of the in vitro genetic toxicity of 4-(2, 4-dichlorophenoxy)butyric acid

The herbicide 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB) is principally used in the USA on peanuts, soybeans and alfalfa. In Europe, it is used on undersown spring barley and grassland (with clover). The genetic toxicity in vitro of the dimethylamine salt of 2,4-DB was examined by employing a range of end points including gene mutation in bacteria (Ames test) and mammalian cell cultures (CHO/HGPRT assay), cytogenetic abnormalities in mammalian cells (CHO/chromosomal aberration assay), and induction of DNA damage and repair in rat hepatocytes. There were no indications of genotoxic potential for 2,4-DB in the first three of these assays. One of the two criteria for a positive response in the UDS assay was exceeded but the increases did not exceed the second criteria for a positive response. The test material was therefore evaluated as weakly active in this assay. The weight of the evidence clearly indicates that 2, 4-DB is not genotoxic to mammals and are consistent with the reported lack of carcinogenic potential for 2,4-DB in both mice and rats.

Genotoxicity testing of six insecticides in two crosses of the Drosophila wing spot test

Among the great variety of genotoxicity assays available, the wing spot test in Drosophila melanogaster has some characteristics that make it very suited for the screening of genotoxic activity, i.e., it is an easy and inexpensive assay using a eukaryotic organism in vivo. One of the most interesting characteristics of the assay is its capacity to detect genotoxic activity of promutagens without the necessity of an exogenous metabolic activation system. In this paper we present results obtained with a recently developed high bioactivation cross of the wing spot test (NORR cross). The positive results obtained with the five well-known procarcinogens 7, 12-dimethylbenz[a]anthracene, N-nitrosopyrrolidine, p-dimethylaminoazobenzene, diethylnitrosamine and urethane clearly show that the NORR strains are similar to the other high bioactivation strains previously described, but they lack their methodological disadvantages. We have tested six insecticides, which are characterised by having contradictory results in other genotoxicity tests, using both the standard and the high bioactivation (NORR) cross. The six insecticides analysed are the pyrethroid allethrin, the methylenedioxyphenolic compound piperonyl butoxide, the chlorinated hydrocarbons dieldrin and endrin, and the organophosphates dimethoate and malathion. We obtained negative results for all six compounds. Our results show the suitability of the wing spot test for the evaluation of compounds at the first level of genotoxicity testing.

In situ assessment of pesticide genotoxicity in an integrated pest management program I--Tradescantia micronucleus assay

The genotoxicity induced by pesticides applied in an integrated pest management (IPM) program was evaluated with the Tradescantia micronucleus assay (Trad-MCN). Three pesticide application rates were prescribed as follows: (a) Low, no field pesticide spray; (b) Medium, IPM test rate: banded cyanazine plus metolachlor (2.7 kg a.i. and 2.3 l a.i./ha of herbicides, respectively); and (c) High, a preventative pesticide application program: broadcast cyanazine plus metolachlor (same application rates as above) plus chlorpyrifos (1 kg a.i./ha of insecticide). The Trad-MCN was employed for the assessment of (a) the formulated compounds, singly and in combinations; (b) pesticide residues extracted from soils sampled before and after application, and (c) in situ exposures (14-h exposure to pesticide-sprayed field). All pesticides showed clastogenic potency at doses between 10 and 50 ppm. Aqueous extracts of the two pesticide-sprayed soils were clastogenic, but the unsprayed soil extracts were not. Plants exposed in situ to pesticide-sprayed soils (inside a chamber receiving vapors from the soil) also showed significant increases in micronuclei frequency in relation to controls exposed to unsprayed soil. In general, there was no significant reduction in the genotoxic effects from the High to the Medium treatment levels of the IPM program. This suggests that the reduction in pesticide application rates attained with the implementation of the proposed IPM program was not sufficient to abate the genotoxicity of the pesticides, as perceived with the sensitive assays employed. The results indicate that replacing genotoxic compounds may be the only effective remediation measure to eliminate the risks imposed by mutagenic compounds in the agricultural environment.

In situ assessment of pesticide genotoxicity in an integrated pest management program: II. Maize waxy mutation assay

The mutagenicity induced by pesticides applied in an integrated pest management (IPM) program was evaluated in situ with the maize forward waxy mutation bioassay. Three pesticide application rates were prescribed as follows: (1) Low--no field pesticide spray; (2) Medium--IPM test rate: banded cyanazine plus metolachlor (2.7 kg a.i. and 2.3 l a.i./ha of herbicides, respectively); and (3) High--a preventative pesticide application program: broadcast cyanazine plus metolachlor (same application rates as above) plus chlorpyrifos (1 kg a.i./ha of insecticide). In general, there was no significant reduction in the genotoxic effects from the high to the medium treatment levels of the IPM program. This suggests that the reduction in pesticide application rates attained with the implementation of the proposed IPM program was not sufficient to abate the genotoxicity of the pesticides. The results indicate that replacing genotoxic compounds may be the only effective remediation measure if concern about environmental mutagenesis were to result in changes in agricultural management.

Organochlorine pesticide accumulation and genotoxicity in Mexican free-tailed bats from Oklahoma and New Mexico

The summer population of Mexican free-tailed bats (Tadarida brasiliensis) at Carlsbad Caverns, New Mexico, declined from an estimated 8.7 million in 1936 to 200,000 in 1974; thereafter, it increased to approximately 700,000 in 1991. This decline has been attributed primarily to organochlorine (OC) pesticide contamination and habitat disturbance. Similar declines have been observed in other populations of this species. This study examined the potential genotoxic effects of OC pesticide contamination on two populations of T. brasiliensis. Pesticide accumulation, frequencies of chromosomal aberrancy, and nuclear DNA content variation in spleen and testicular tissues were examined in specimens collected from Carlsbad Caverns and Vickery Cave, a maternity colony in northwestern Oklahoma, during the summers of 1990 and 1991. Pesticide residues in brain and carcass tissues were identified and quantified by electron capture gas chromatography. Genotoxicity was examined with the standard bone marrow chromosomal aberration assay and flow cytometry. Statistical relationships among pesticide content, observed chromosomal aberrancy, and nuclear DNA content variation were examined. Both populations demonstrated significant levels of DDE contamination; however, the Carlsbad Caverns population showed consistently higher pesticide loads. Males also demonstrated higher levels than females. No statistical differences in chromosomal aberrancy or nuclear DNA content variation were observed among sexes, sites, or collected periods. Positive correlations were detected between brain and carcass DDE concentrations for all bats examined. A significant negative relationship was found between brain DDE concentration and coefficients of variation in spleen DNA content only for males.

Flow cytogenetic analysis of whole cell clastogenicity of herbicides found in groundwater

Agronomic practices followed in recent years have caused the agrarian sector to depend heavily on agri-chemicals such as herbicides, but herbicides have negative environmental consequences. Their usage has resulted in chemicals being introduced into the groundwater. Although the contaminants are in trace amounts, little is known about their potential clastogenic effects at low concentrations. In the present study, the potential of flow cytometric analysis to detect the whole cell clastogenic properties of low level chemical exposure is examined. Chinese Hamster Ovary (CHO) cells were exposed to three herbicides (atrazine, bentazon and simazine) and two known clastogens (adriamycin and ara-C) at low concentrations for 48 h. Nuclei were isolated from control as well as treatments and analyzed by flow cytometry. The clastogenic property was assessed by measuring the coefficient of variation (CV) of G1 peaks in different treatments. Exposure to known clastogens resulted in increasing CVs with increasing concentrations. Flow cytometry was a very accurate and sensitive technique for the whole cell clastogenic assay. The results indicated that atrazine has the potential to cause whole cell clastogenicity, even at a very low concentration. Bentazon showed indications of clastogenic potential but the increases in CVs observed with this herbicide were not statistically significant. The CVs are unaffected by simazine exposure, thus indicating that simazine does not cause whole cell clastogenesis under short term exposure. Flow cytometry proved to be an excellent tool for assaying the clastogenic potential of agri-chemicals.

Structure-activity relationships (SARs) among mutagens and carcinogens: a review

This review is an introduction to methods for evaluating structure-activity relationships (SARs), and, in particular, to those methods that have been applied to study mutagenicity and carcinogenicity. A brief history and some background material on the earliest attempts to correlate molecular structure and biological activity are included. Most of the discussion focuses on modern methods utilizing extrathermodynamic and physical property variables such as the Hansch method and SIMCA, and approaches based on molecular connectivity such as the ADAPT, CASE, and Enslein methods. In general, the latter class is potentially the most useful in the study of the large and structurally diverse databases so often encountered in the study of mutagenicity and carcinogenicity. They also are not very sensitive to lab-to-lab variances in reported activities and outright misclassifications in activities of some compounds. This is chiefly because the statistical treatments used in these methods tend to dilute the importance of outliers. The methods using physicochemical and extrathermodynamic variables are especially important in relatively small, congeneric databases and can help fine-tune the role of physicochemical properties in mechanistic hypotheses. All of the above methods have been used to look at mutagenicity and carcinogenicity and some of the results reported in the literature are reviewed here. As far as specific methods go, ADAPT, CASE, SIMCA and the Enslein approach all seem to have similar classification powers (in the range of 75-95%), depending very much on the database studied. The emphasis in this review is on showing that the use of these computer-aided storage, retrieval and analysis techniques is a timely approach to predicting and even understanding the toxicity of environmental substances. However, each of the methods discussed is still under development, and their potential usefulness for predictive purposes is still being explored.

Evaluation of the genotoxic potential of certain pesticides used in Pakistan

The mutagenicity of fifteen insecticides, five fungicides, four herbicides, and an acaricide commonly used in Pakistan was evaluated by employing thirteen short-term bioassays. The genetic endpoints used included point or gene mutation, primary DNA damage, and chromosomal effects. Initially, all pesticides were tested in a "core" battery of four in vitro bioassays. A carefully selected group among these chemicals was retested in higher level test systems to confirm the results obtained in the initial phase. Of the pesticides tested, only a small portion consistently displayed mutagenicity across test systems. The Saccharomyces cerevisiae bioassays detected mutagenicity for the largest number of pesticides. The Salmonellaces typhimurium strain, TA100, was able to detect genetic activity in all of the pesticides that produced positive results in this bioassay. The cytogenetic effects observed from the Vicia faba root assay were consistent with those obtained in mammalian cells in culture. All pesticides which displayed mutagenicity were not carcinogenic in animal bioassays but, in general, mutagenicity in a battery of short-term bioassays was a reliable indicator of the carcinogenic potential in animals. A simple test battery is proposed for evaluating the genetic potential of agricultural pesticides.

Genotoxicity of methyl parathion in short-term bacterial test systems

Genotoxicity of the insecticide methyl parathion was investigated in Salmonella typhimurium and Escherichia coli bacterial test systems for the detection of back mutations and DNA-damage. Methyl parathion was mutagenic to S. typhimurium strain TA100 after activation with rat liver microsomal and cytosolic enzymes. In DNA repair tests, methyl parathion was effective in inducing damage to the S. typhimurium strain TA1538 which lack excision repair compared to the strain TA1978 which is proficient in excision repair mechanisms. Normal laboratory light conditions had no effect on the mutagenicity tests, however, exposure of methyl parathion in the petri dish containing the tester strain TA100 and rat liver microsomal and cytosolic enzymes reduced the mutagenic activity and increased the toxic effects of methyl parathion.