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Differential sensitivity of two green algae, Scenedesmus obliqnus and Chlorella pyrenoidosa, to 12 pesticides.

Growth-inhibiting tests were carried out for 12 pesticides (including 11 fungicides: fosetyl-aluminum, benomyl, metalaxyl, iprodione, dimetachlone, carbendazim, thiophanate-methyl, bismerthiazol, procymidone, zineb, chlorothalonil, and the acaricide abamectin) in the green algae Chlorella pyrenoidosa and Scenedesmus obliqnus and the differential sensitivities of the two green algae to those pesticides were compared. The results indicate that the acute toxicity of benomyl to C. pyrenoidosa and S. obliqnus is the highest among all of the pesticides tested and is close to that of the photosynthesis-inhibiting herbicides atrazine, simazine, and chlorotoluron. Meanwhile, algal species vary widely in their response to the pesticides. The results demonstrated that there was a differential response to various pesticides by the two species of algae and that the sensitivity of various species of algae exposed to chlorothalonil varied by nearly two orders of magnitude; sensitivity to thiophanate-methyl varied by more than one order. Investigations using different algal species as test organisms have demonstrated that algae vary greatly in their response to chemicals. Differential sensitivity of green species to the compounds could induce species shifts within communities.

Biological Assay↗

Assessment of the reproductive and developmental toxicity of pesticide/fertilizer mixtures based on confirmed pesticide contamination in California and Iowa groundwater.

Pesticides and fertilizers, as used in modern agriculture, contribute to the overall low-level contamination of groundwater sources. In order to determine the potential of pesticide and fertilizer mixtures to produce reproductive or developmental toxicity at concentrations up to 100 x the median level found in groundwater, we prepared and studied two mixtures of pesticides and a fertilizer (ammonium nitrate). One mixture containing aldicarb, atrazine, dibromochloropropane, 1,2-dichloropropane, ethylene dibromide, and simazine plus ammonium nitrate was considered to be a representative of groundwater contamination in California (CAL). The other, containing alachlor, atrazine, cyanazine, metolachlor, metribuzin, and ammonium nitrate, simulated groundwater contamination in Iowa (IOWA). Each mixture was administered in the drinking water of either Swiss CD-1 mice during a Reproductive Assessment by Continuous Breeding study or pregnant Sprague-Dawley rats (gd 6-20) at three dose levels (1x, 10x, and 100x) where 1x was the median concentration of each pesticide component as determined in the groundwater surveys in California or Iowa. Unlike conventional toxicology studies, the purpose of this study was to evaluate the health effects of realistic human concentrations. Thus, the testing concentrations are probably well below the maximally tolerated dose. Propylene glycol was used as the solubilizer for the pesticides in drinking water formulations in both studies. In the reproductive study, neither mixture caused any clinical signs of toxicity, changes in food or water consumption, or body weight in either F0 or F1 mice at doses up to 100x the median groundwater concentrations. There were no treatment-related effects on fertility or any measures of reproductive performance of either the F0 or the F1 generation mice exposed to either CAL or IOWA at up to 100x. Similarly, measures of spermatogenesis, epididymal sperm concentration, percentage motile sperm, percentage abnormal sperm, and testicular and epididymal histology were normal. In the developmental study, CAL- or IOWA-exposed females did not exhibit any significant treatment-related clinical signs of toxicity. No adverse effects of CAL or IOWA were observed for measures of embryo/fetal toxicity, including resorptions per litter, live litter size, or fetal body weight. CAL or IOWA did not cause an increased incidence of fetal malformations or variations. In summary, administration of these pesticide/fertilizer mixtures at levels up to 100-fold greater than the median concentrations in groundwater supplies in California or Iowa did not cause any detectable reproductive (mice), general, or developmental toxicity (rats).

Animals↗

Evaluation of atrazine soil extraction methods for the determination by enzyme immunoassay and gas chromatography.

Four soil extraction methods were evaluated for the determination of atrazine and other s-triazines by ELISA and GC, using both field-treated and laboratory fortified samples. The most efficient recoveries for atrazine, simazine, and cyanazine from loam soil fortified at concentrations from 0.01 ppm to 1 ppm were obtained by mechanical wrist-action shaker (1 h) using methanol:water and solid phase extraction (SPE) cleanup (standard method). A handshaking extraction (1 min) with acetonitrile:water showed fairly good correlation with the standard extraction method and is suitable for field use with ELISA. Sonication using acetonitrile:water and SPE cleanup was the most efficient extraction method for the dealkylated metabolites (deisopropyl and deethyl atrazine) with recoveries higher than 60%. In general, supercritical fluid extraction (SFE) was as efficient as sonication and handshaking but was more variable. A guideline for validation of immunoassays and methods comparison is given. The sensitivity of the ELISA method was comparable to the GC and was both accurate and precise. Comparison of ELISA and GC determinations of 120 field soil samples and 40 laboratory spiked soil samples extracted with four different methods showed no false negatives or positives with excellent correlations and showed not significant differences (P > 0.05). An evaluation of the cost for GC and ELISA methods was also conducted.

Atrazine↗

Analysis of triazine herbicides residues in butter and pasteurized milk.

A method has been developed for the determination of atrazine, cyanazine, prometryn, simazine, and terbutryn residues in butter. The residues were extracted from the matrix with a mixture of petroleum ether/methanol (3 + 1), and from the separated water-methanol phase extraction was carried out with chloroform. The extract was cleaned up on an alumina column. Capillary glass liquid chromatography using a 15 m x 0.32 mm glass capillary column coated with OV-1 and an alcali flame ionization detector were employed for the analysis of the residues. The analyses were evaluated by the internal standard method, using metribuzin as the internal standard. The recovery of the method was 68.7%-79.8% for the individual herbicides under study at the fortification level of 0.1 mg.kg-1 and 79.2%-91.9% at the fortification level of 0.02 mg.kg-1. The determination limit of the method was 0.005 mg.kg-1. When centrifuging full milk, residues of triazines were partitioned between the water and fat phases, whereby 17%-82% of the residues were transferred to the milk fat. Samples of commercial butter were analysed and found to contain 0.005-0.023 mg.kg-1 atrazine.

Animals↗

Pesticide and polychlorinated biphenyl residues in waters at the mouth of the Grand, Saugeen, and Thames Rivers, Ontario, Canada, 1986-1990.

Water samples were collected from the mouths of the three major agricultural watersheds, the Grand, the Saugeen, and the Thames (Ontario, Canada), between January 1986 and December 1990. Analyses were performed for 18 herbicides, 26 insecticides, and 4 fungicides in use in the basins. A total of between 425 and 474 samples were analyzed for each of the major groups of pesticides. Six herbicides, two insecticides and polychlorinated biphenyls (PCBs) were identified in surface water. Atrazine and its metabolite desethylatrazine were the most frequently found pesticide present in 340 of 474 samples or 72%; the metabolite was not always present with the parent compound. The second most frequently found pesticide was metolachlor which was identified in 30 of 474 samples or 6.3%. 2,4-D and cyanazine were present in 3.3% and 1.5% of the samples, respectively; alachlor, mecoprop, and simazine were present in 0.5% of the samples. Dicamba and metribuzin were present in single samples (0.2%). DDT, heptachlor epoxide, and PCB were identified in only single samples over the 5-year period. Between 342 and 2959 kg/annum of total atrazine were found passing the mouth of the three rivers and entering Lakes Erie or St. Clair between 1986 and 1990. The greatest loss was from the Thames River and the least from the Saugeen River. Between 1% and 2% of that applied in the watershed was lost at the mouth. Loadings of only two other pesticides to the rivers exceeded 5 kg in any one year, namely, metolachlor and 2,4-D. In the case of metolachlor, loadings ranged from less than 5 to 1,726 kg/annum, the highest being in the Thames and the lowest in the Saugeen River. 2,4-D exceeded a loading of 5 kg/annum in 1988 in the Grand River. Atrazine, cyanazine, and metolachlor were tracked across Lake St. Clair from the mouth of the Thames to the mouth of the Detroit River in 1987.

Ontario↗

Use of gas liquid chromatography/mass spectrometry for triazine herbicide residues analysis in forage and milk.

Residual s-triazines were isolated from forage and milk samples by methanol/chloroform extraction followed by column purification. The evaporated extracts were dissolved in acetone and analysed by gas chromatography with NPD detection and mass spectrometry. The detection limits for both methods were found to be about 5 approximately 10 ng of each s-triazine. The selective ions of the 10 s-triazines investigated (simazine, atrazine, propazine, terbuthylazine, cyanazine, desmetryne, ametryne, prometryne, terbutryne and methoprotryne) were chosen on the basis of an electron impact mass spectrometry study of the s-triazine standards and the whole mass spectra are given. Special attention was paid to the fragmentation of cyanazine and the general cleavage pathways of the s-triazines under investigation.

Animal Feed↗

The role of organic colloids in herbicide transfer to rivers: a quantitative study of triazine and phenylurea interactions with colloids.

For moderately hydrophobic compounds such as most pesticides adsorption on colloids (<0.2 microm) may play a key role in pesticide mobility as well as in their degradation by chemical and microbiological processes. However, until now, pesticide-organic colloid interactions are poorly understood. Quantitative data for sorption equilibria on colloids of two series of herbicides including triazines (atrazine, simazine, terbutylazine, prometryne, desethylatrazine, and desisopropylatrazine) and phenylureas (isoproturon, linuron, neburon, and diuron) sampled in the Seine river (urban zone) and the Marne river (agricultural zone) are presented. Partition coefficient of herbicides on colloids (K(com)), were evaluated by solid-phase extraction coupled with high-performance liquid chromatography-UV diode-array detection (SPE-HPLC-UV/DAD). In the case of triazines a satisfactory log-log correlation was found between K(com) and octanol-water coefficient (K(ow)) values. Phenylureas did not obey this correlation, with K(com) values being about two times higher than those of triazines. The existence of two distinct types of adsorption behaviour on colloids partly explains the different occurrence of triazines and phenylureas in surface waters.

Adsorption↗

Clean-up of triazines in vegetable extracts by molecularly-imprinted solid-phase extraction using a propazine-imprinted polymer.

An analytical methodology based on a molecularly imprinted solid-phase extraction (MISPE) procedure was developed for the determination of several triazines (atrazine, simazine, desethylatrazine (DEA), desisopropylatrazine (DIA), and propazine) in vegetable samples. A methacrylic acid-based imprinted polymer was prepared by precipitation polymerisation using propazine as template and toluene as porogen. After removal of the template by Soxhlet extraction, the optimum loading, washing, and elution conditions for MISPE of the selected triazines were established. The optimised MISPE procedure was applied to the extraction of the selected triazines in pea, potato, and corn sample extracts and a high degree of clean-up was obtained. However, some remaining interferences, non-specifically and strongly bound to the polymeric matrix, appeared in the chromatogram, preventing quantification of DIA in potatoes and DIA, DEA, and propazine in corn samples. Thus, a new clean-up protocol based on the use of a non-imprinted polymer for removal of these interferences prior to the MISPE step was developed. By following the new two-step MISPE procedure, the matrix compounds were almost completely removed, allowing the determination of all the triazines selected at concentration levels below the established maximum residue limits, making the developed procedure suitable for monitoring these analytes in vegetable samples.

Chromatography, High Pressure Liquid↗

Generation of antiserum to Irgarol 1051 and development of a sensitive enzyme immunoassay using a new heterologous hapten derivative.

A polyclonal antiserum to Irgarol 1051 was developed in sheep and used to construct an enzyme immunoassay method for the measurement of the antifouling compound in river and seawater samples. The antiserum was generated by a hapten derivative, 2-(tert-butylamino)-4-(cyclopropylamino)-6-(thiopropionic acid)-1,3,5-triazine, coupled to a mixture of keyhole limpet hemocyanin and bovine serum albumin, and the competitive enzyme immunoassay was constructed using a plate-coating antigen made of a heterologous new hapten derivative, 2-(tert-butylamino)-4-(cyclopropylamino)-6-(phenoxybenzoic acid)-1,3,5-triazine, linked to gelatine. The assay showed a sensitivity of about 5 ng L(-1) in river and seawater matrices with reasonable specificity with respect to commonly used triazines such as atrazine (3%), simazine (>0.1%) and desethylatrazine (>0.01%). However, high cross-reactivity levels were found with ametryn (56%) and prometryn (60%). Tests on the effects of organic solvents on assay performance indicated a high tolerance to methanol but much less so to acetonitrile. The assay was found to be highly reproducible and robust owing to the stability of the sheep antibody and the highly optimised competitive assay reagents which included the use of the new triazine-O-phenoxybenzoic acid derivative.

Haptens↗

Tyrosinase inhibition organic phase biosensor for triazinic and benzotriazinic pesticide analysis (part two).

Several triazine pesticides, such as atrazine, are much more soluble in several organic solvents, such as chloroform, than in water. Our recent research was aimed at analyzing this class of pesticides using tyrosinase OPEE (organic phase enzyme electrodes), exploiting their inhibiting action on the tyrosinase enzyme when operating in water-saturated chloroform medium. In this work we studied the response of a tyrosinase inhibition enzyme sensor to several triazinic (simazine, propazine, terbuthylazine) and benzotriazinic (azinphos-ethyl and azinphos-methyl) pesticides (LOD=0.5x10(-9) mol l(-1)). Recovery trials were also performed in vegetal matrixes (corn, barley, lentils). Lastly, the effect of the solvent (chloroform or water) on the inhibition process was investigated via Hill's equation and the diffusion of analyte from the solvent to the enzyme membrane.

Biosensing Techniques↗

Polar herbicides, pharmaceutical products, perfluorooctanesulfonate (PFOS), perfluorooctanoate (PFOA), and nonylphenol and its carboxylates and ethoxylates in surface and tap waters around Lake Maggiore in Northern Italy.

A survey of contamination of surface and drinking waters around Lake Maggiore in Northern Italy with polar anthropogenic environmental pollutants has been conducted. The target analytes were polar herbicides, pharmaceuticals (including antibiotics), steroid estrogens, perfluorooctanesulfonate (PFOS), perfluoroalkyl carboxylates (including perfluorooctanoate PFOA), nonylphenol and its carboxylates and ethoxylates (NPEO surfactants), and triclosan, a bactericide used in personal-care products. Analysis of water samples was performed by solid-phase extraction (SPE) then liquid chromatography-triple-quadrupole (tandem) mass spectrometry (LC-MS-MS). By extraction of 1-L water samples and concentration of the extract to 100 microL, method detection limits (MDLs) as low as 0.05-0.1 ng L(-1) were achieved for most compounds. Lake-water samples from seven different locations in the Southern part of Lake Maggiore and eleven samples from different tributary rivers and creeks were investigated. Rain water was also analyzed to investigate atmospheric input of the contaminants. Compounds regularly detected at very low concentrations in the lake water included: caffeine (max. concentration 124 ng L(-1)), the herbicides terbutylazine (7 ng L(-1)), atrazine (5 ng L(-1)), simazine (16 ng L(-1)), diuron (11 ng L(-1)), and atrazine-desethyl (11 ng L(-1)), the pharmaceuticals carbamazepine (9 ng L(-1)), sulfamethoxazole (10 ng L(-1)), gemfibrozil (1.7 ng L(-1)), and benzafibrate (1.2 ng L(-1)), the surfactant metabolite nonylphenol (15 ng L(-1)), its carboxylates (NPE(1)C 120 ng L(-1), NPE(2)C 7 ng L(-1), NPE(3)C 15 ng L(-1)) and ethoxylates (NPE( n )Os, n = 3-17; 300 ng L(-1)), perfluorinated surfactants (PFOS 9 ng L(-1), PFOA 3 ng L(-1)), and estrone (0.4 ng L(-1)). Levels of these compounds in drinking water produced from Lake Maggiore were almost identical with those found in the lake itself, revealing the poor performance of sand filtration and chlorination applied by the local waterworks.

Caprylates↗

Oil-in-water emulsions as suitable working media for the direct polarographic determination of aziprotryne and desmetryne from its organic extracts in water samples.

The electroanalytical behavior of the reduction of the herbicides aziprotryne (2-azido-4-isopropylamino-6-methylthio-1,3,5-triazine) and desmetryne (4-isopropylamino-6-methylamino-2-methylthio-1,3,5-triazine) in oil-in-water emulsions is reported. This medium allows the differential pulse polarographic determination of these s-triazines directly from their sample extracts in an appropriate organic solvent. Sodium pentanesulfonate was chosen as the most suitable surfactant to be used as emulsifying agent, whereas ethyl acetate was selected as the organic solvent to form the emulsions. The peak current was maximum in a 0.3 mol L(-1) HClO4 medium of the continuous aqueous phase for aziprotryne, and at pH 3.0 for desmetryne, and the potential became more negative as the pH increased for both herbicides. The limiting current is diffusion controlled and the electrode process is irreversible. Four electrons are involved in the overall electrochemical reduction process as determined by controlled potential coulometry, whereas the alpha n(a) values suggested that two electrons are involved in the rate-determining step. Using differential pulse polarography, aziprotryne and desmetryne can be determined in the emulsified medium over the concentration ranges 1.0 x 10(-7)-1.0 x 10(-4) mol L(-1), with limits of detection of 4.5 x 10(-8) mol L(-1) and 6.6 x 10(-8) mol L(-1), respectively. The method was applied to the determination of aziprotryne and desmetryne in spiked irrigation water. At concentration levels of 6.0 x 10(-7) mol L(-1) aziprotryne and 4.0 x 10(-7) mol L(-1) desmetryne, recoveries of 94 +/- 3% and 94 +/- 4%, respectively, were obtained after preconcentration on Sep-Pack C18 cartridges. Finally, partial least-squares regression (PLSR) has been used for treatment of the polarographic data obtained from mixtures of aziprotryne, desmetryne and simazine in oil-in-water emulsions. The size of the calibration set was of 29 samples by ninety two current measurements at different potentials. Prediction of the herbicides concentration within the range 1.0 x 10(-6)-1.0 x 10(-5) mol L(-1) was possible.

Calibration↗

Joint toxicity of triazine herbicides and organophosphate insecticides to the midge Chironomus tentans.

A series of recent studies demonstrated that the triazine herbicide atrazine, although not itself acutely toxic, potentiated the toxicity of certain organophosphate insecticides (OPs) to the midge Chironomus tentans. In the current study, a series of triazine herbicides and triazine herbicide degradation products were tested to determine if other triazines potentiate OP toxicity to midges. Chlorpyrifos and diazinon were the OPs tested. Toxicity tests were conducted using a factorial design and analysis of variance to statistically determine if each triazine had an effect on expected toxicity. Log-probit procedures were also used to evaluate the magnitude of change in median effective concentration (EC50) values during coexposure with each triazine. All of the triazine herbicides tested (atrazine, simazine, cyanazine, and hexazinone) were capable of potentiating the toxicity of the OPs, whereas the degradation products (s-triazine, deethylatrazine, and deisopropylatrazine) had less effect. In most cases, a triazine concentration of 100 microg/L was necessary to significantly increase OP toxicity, and higher concentrations of triazine caused a greater degree of potentiation. Changes in EC50 values ranged from no change to a 2.5-fold increase in toxicity. Generally, EC50 values changed by less than a factor of 2, indicating that the effect may be of limited concern in regard to future risk assessments of OPs.

Animals↗

Effects of triazine herbicides on organophosphate insecticide toxicity in Hyalella azteca.

The frequent use of pesticides in agricultural and commercial settings has led some researchers to devote their attention to studying the effects of mixtures of these compounds as they co-occur in the environment. Recent studies have demonstrated the potentiating effects of triazine herbicides, such as atrazine and its analogs, to the toxicity of a variety of organophosphate (OP) insecticides. One such OP insecticide, chlorpyrifos, has been the topic of much concern because of its prevalence in the environment. This study focused on examining the effects of 10 select triazine herbicides at concentrations of 1 mumole/L (approximately 200 mug/L) to chlorpyrifos with Hyalella azteca. The compounds selected include atrazine, three of its degradation products, and six other herbicide active ingredients. Toxicity tests were performed using a two-way analysis of variance matrix design with effect levels determined by way of probit analysis. Atrazine was found to have the greatest acutely lethal effect to H. azteca, followed by its closest degradation product, deethylatrazine. Two of the six atrazine analogs, simazine and cyanazine, also showed significant effects to the insecticide's toxicity. Synergistic ratios (SRs) were calculated to compare the effect magnitudes for each of the herbicides. The highest ratio obtained was with atrazine (SR = 1.42). A majority of the past studies involving mixtures of triazines and OPs have examined the potentiation effects of active-use triazine herbicides on Chironomus species. However, compared with the acute effects previously obtained for Chironomus species, H. azteca show a higher tolerance to the presence of the triazine herbicides, even at levels often considered as being at the high end of environmentally relevant concentrations. When coupled with past studies from our laboratory, this research helps to provide a better understanding of the toxic effects of herbicide-insecticide interactions.

Amphipoda↗

Pesticides in canals of South Florida.

Atrazine, ametryn, bromacil, simazine and norflurazon were the most frequently detected pesticides in surface water samples and DDE, DDD and ametryn were the most frequently detected pesticides in sediment samples collected over the period November 1991 to June 1995 in a monitoring network that includes 27 stations in south Florida canals. The 744 pesticide detections during this time period represent about 2% of the total number of analytical determinations. Many of the most frequently detected compounds were used in large amounts in the monitoring area based on pesticide usage estimates included in this study. Spatial trends in pesticide detections followed use patterns. The maximum atrazine detections occurred in winter to late spring and were associated with usage on turfgrass and agricultural products. Endosulfan residues above the Florida water quality criterion were occasionally observed in surface water in the Homestead area and most of the exceedences occurred in confined waters. Methods with lower MDLs have recently been developed and should increase the number of detections in future sampling. Pesticides which bind strongly to soil, pesticides that are highly persistent and those used in large amounts were some of the more frequently found pesticides in sediments.

Environmental Monitoring↗

Biodegradation of triazine herbicides on polyvinylalcohol gel plates by the soil yeast Lipomyces starkeyi.

The soil yeast Lipomyces starkeyi was tested for its ability to degrade triazine herbicides. Polyvinylalcohol (PVA) was employed as a solid medium in culture plates instead of agar. The cell sizes of the control (without nitrogen source) on the PVA gel plate were much smaller than those on the agar gel plate. The difference between the diameters of the sample and control colonies on the PVA gel plate were almost twice those of the colonies on the agar gel plate (1.9 and 1.0 mm, respectively). Thus, the PVA gel plate is much better than the agar plate for evaluating the degree of utilization of a sole nitrogen source. The yeast grew well (more than 4 mm in diameter) with 1,3,5-triazine or cyanuric acid as nitrogen source. In addition, melamine and thiocyanuric acid inhibited growth of the yeast, and the sizes of colonies were smaller than those of the control. All triazine herbicides tested (simazine, atrazine, cyanazine, ametryn, and prometryn) could be degraded and assimilated by L. starkeyi.

Agar↗

Inhibition of atrazine degradation by cyanazine and exogenous nitrogen in bacterial isolate M91-3.

A variety of s-triazine herbicides and nitrogen fertilizers frequently occur as co-contaminants at pesticide manufacturing and distribution facilities. The degradation of atrazine and cyanazine by the bacterial isolate M91-3 was investigated in washed-cell suspensions and crude cellular extracts. Cyanazine competitively inhibited atrazine degradation. The maximum atrazine degradation rate (Vmax) was 41 times higher and the half-saturation constant for the inhibitor (Ki) was 1.3 times higher in the crude cellular extract than in the washed-cell suspension, suggesting that cellular uptake influenced degradation of the s-triazines. Cultures that had received prior exposure to atrazine and simazine exhibited comparable atrazine degradation rates, while cells exposed to cyanazine, propazine, ametryne, cyanuric acid, 2-hydroxyatrazine, biuret, and urea exhibited a lack of atrazine-degradative activity. Growth in the presence of exogenous inorganic nitrogen inhibited subsequent atrazine-degradative activity in washed-cell suspensions, suggesting that regulation of s-triazine and nitrogen metabolism are linked in this bacterial isolate. These findings have significant implications for the environmental fate of s-triazines in agricultural settings since these herbicides are frequently applied to soils receiving N fertilizers. Furthermore, these results suggest that bioremediation of s-triazine-contaminated sites (common at pesticide distribution facilities in the cornbelt) may be inhibited by the presence of N fertilizers that occur as co-contaminants.

Atrazine↗

Identification of bacteria isolated from an oligotrophic lake with pesticide removal capacities.

We studied the growth and capacities for pesticides removal of bacterial strains isolated from the Laguna Grande, an oligotrophic lake at the South of Spain (Archidona, Málaga). Strains were isolated from water samples amended with 10 and 50 microg/ml of nine pesticides: organochlorinated insecticides (aldrin and lindane), organophosphorous insecticides (dimetoate, methyl-parathion and methidation), s-triazine herbicides (simazine and atrazine), fungicide (captan) and diflubenzuron (1-(-4-chlorophenyl)-3-(2,6-difluorobenzoyl urea), a chitinase inhibitor. The majority of the strains belonged to the genera Pseudomonas and Aeromonas and only 9% of the total of strains were Gram positive. From all the strains isolated, only 22 showed a wide growth range in all the pesticides tested and 4 of them were chosen for pesticide removal studies. The genetic identification of these strains showed their affiliation to Pseudomonas pseudoalcaligenes, Micrococcus luteus, Bacillus sp. and Exiguobacterium aurantiacum. These last two strains were those that showed the highest pesticide removal capacities and a high bacterial growth.

Aeromonas↗