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 μmole/L (approximately 200 μg/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.     

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.     

Toxicity of the Insecticide Terbufos,its Oxidation Metabolites,and the Herbicide Atrazine in Binary Mixtures to <Emphasis Type="Italic">Ceriodaphnia</Emphasis> cf <Emphasis Type="Italic">dubia</Emphasis>

The acute toxicity of terbufos and its major metabolites, tested alone, in binary mixtures or in combination with atrazine were evaluated using neonates of the cladoceran Ceriodaphnia cf dubia. Terbufos, terbufos sulfoxide, and terbufos sulfone tested individually were highly toxic to C. cf dubia, with mean 96-h EC₅₀ values of 0.08, 0.36, and 0.19 μg/l, respectively. The addition of atrazine (10 μg/l) significantly increased the toxicity of terbufos. The toxicity of terbufos sulfone was unaffected by atrazine, whereas the results for terbufos sulfoxide were equivocal. Equitoxic mixtures of the metabolites showed additive toxicity to C. cf dubia. The high toxicities of terbufos and its environmentally persistent oxidative metabolites suggest that contamination of aquatic systems with this insecticide mixture and the coapplied herbicide atrazine might pose a greater hazard to some biota than their individual toxicities.     

Toxicity of Atrazine and Molinate to the Cladoceran <Emphasis Type="Italic">Daphnia carinata</Emphasis> and the Effect of River Water and Bottom Sediment on Their Bioavailability

Atrazine and molinate are widely used herbicides and concern has been raised about their potential deleterious impacts on aquatic ecosystems. Although there have been some studies on the toxicity of herbicides to aquatic organisms using laboratory or natural water, information on the effect of sediments, suspended particulates, and dissolved organic matter on their bioavailability is quite limited. This study aims to provide toxicity data that considers these factors and the effect that these factors have on bioavailability. In this study, the toxicity of the test chemicals was calculated following the Organisation for Economic Co-operation and Development (OECD) methods, whereas change in bioavailability was measured using EC₅₀ values based on measured initial concentrations of the test chemicals. The acute (48-h) static toxicity of atrazine and molinate to the freshwater cladoceran Daphnia carinata was determined in cladoceran water and river water in the absence and presence of sediment. The 48-h EC₅₀ (immobilization) values of atrazine to D. carinata ranged from 22.4 to 26.7 mg/L, while the corresponding values for molinate ranged from 18.3 to 33.6 mg/L, respectively. Both chemicals were classed as having low acute toxicity to D. carinata. The presence of dissolved organic matter and suspended particles in river water did not significantly (p > 0.05) reduce the bioavailability (measured as toxicity) of atrazine to D. carinata compared to that tested in cladoceran water. The presence of sediment, however, signifi- cantly (p < 0.05) reduced the bioavailability (48-h EC₅₀) of atrazine in cladoceran water, from 24.6 to 30.7 mg/L, and in river water, from 22.4 to 31.0 mg/L. Similarly, the presence of sediment in cladoceran water, significantly (p < 0.05) reduced the bioavailability (48-h EC₅₀) of molinate, from 26.6 to 46.4 mg/L, and in river water, from 22.5 to 45.6 mg/L.     

Increased toxicity to invertebrates associated with a mixture of atrazine and organophosphate insecticides

This study examined the joint toxicity of atrazine and three organophosphate (OP) insecticides (chlorpyrifos, methyl parathion, and diazinon) exposed to Hyalella azteca and Musca domestica. A factorial design was used to evaluate the toxicity of binary mixtures in which the lethal concentration/lethal dose (LC1/LD1, LC5/LD5, LC15/LD15, and LC50/LD50) of each OP was combined with atrazine concentrations of 0, 10, 40, 80, and 200 microg/L for H. azteca and 0, 200, and 2,000 ng/mg for M. domestica. Atrazine concentrations (> or = 40 microg/L) in combination with each OP caused a significant increase in toxicity to H. azteca compared with the OPs dosed individually. Acetylcholinesterase (AChE) activity also was examined for the individual OPs with and without atrazine treatment. Atrazine in combination with each of the OPs resulted in a significant decrease in AChE activity compared with the OPs dosed individually. In addition, H. azteca that were pretreated with atrazine (> or = 40 microg/L) were much more sensitive to the OP insecticides compared with H. azteca that were not pretreated with atrazine before being tested. Topical exposure to atrazine concentrations did not significantly increase OP toxicity to M. domestica. The results of this study indicate the potential for increased toxicity in organisms exposed to environmental mixtures.     

Effects of atrazine and cyanazine on chlorpyrifos toxicity in Chironomus tentans (Diptera: Chironomidae)

Toxicities of two triazine herbicides (atrazine and cyanazine) and an organophosphate insecticide (chlorpyrifos) were evaluated individually and with each herbicide in binary combination with chlorpyrifos using fourth-instar larvae of the aquatic midge, Chironomus tentans. Chlorpyrifos at 0.25 microg/L resulted in an effect in less than 10% of midges in 48-h acute toxicity bioassays. Neither atrazine nor cyanazine alone at relatively high concentrations (up to 1,000 microg/L) caused significant acute toxicity to C. tentans. However, atrazine and cyanazine caused significant synergistic effects on the toxicity of chlorpyrifos when midges were exposed to mixtures of atrazine or cyanazine (10, 100, 1,000 microg/L) with chlorpyrifos (0.25 microg/L). At fixed concentrations (200 microg/L) of the herbicides, toxicity of chlorpyrifos was enhanced by 1.8- and 2.2-fold by atrazine and cyanazine, respectively, at the 50% effective concentration levels. Although atrazine and cyanazine are not effective inhibitors of acetylcholinesterase (AChE) in vitro, the synergism of the two triazine herbicides with chlorpyrifos was associated with increased in vivo inhibition of AChE in midges. We observed a positive correlation between the degree of inhibition of AChE and the concentration of atrazine or cyanazine in the presence of a fixed concentration of chlorpyrifos. It is possible that these herbicides may affect cytochrome P450 enzymes to confer synergistic effects on the toxicity of chlorpyrifos.     

Comparative Sensitivity of Selenastrum capricornutum and Lemna minor to Sixteen Herbicides

Aquatic plant toxicity tests are frequently conducted in environmental risk assessments to determine the potential impacts of contaminants on primary producers. An examination of published plant toxicity data demonstrates that wide differences in sensitivity can occur across phylogenetic groups of plants. Yet relatively few studies have been conducted with the specific intent to compare the relative sensitivity of various aquatic plant species to contaminants. We compared the relative sensitivity of the algae Selenastrum capricornutum and the floating vascular plant Lemna minor to 16 herbicides (atrazine, metribuzin, simazine, cyanazine, alachlor, metolachlor, chlorsulfuron, metsulfuron, triallate, EPTC, trifluralin, diquat, paraquat, dicamba, bromoxynil, and 2,4-D). The herbicides studied represented nine chemical classes and several modes of action and were chosen to represent major current uses in the United States. Both plant species were generally sensitive to the triazines (atrazine, metribuzin, simazine, and cyanazine), sulfonureas (metsulfuron and chlorsulfuron), pyridines (diquat and paraquat), dinitroaniline (trifluralin), and acetanilide (alachlor and metolachlor) herbicides. Neither plant species was uniformly more sensitive than the other across the broad range of herbicides tested. Lemna was more sensitive to the sulfonureas (metsulfuron and chlorsulfuron) and the pyridines (diquat and paraquat) than Selenastrum. However Selenastrum was more sensitive than Lemna to one of two thiocarbamates (triallate) and one of the triazines (cyanazine). Neither species was sensitive to selective broadleaf herbicides including bromoxynil, EPTC, dicamba, or 2,4-D. Results were not always predictable in spite of obvious differences in herbicide modes of action and plant phylogeny. Major departures in sensitivity of Selenastrum occurred between chemicals within individual classes of the triazine, acetanilide, and thiocarbamate herbicides. Results indicate that neither species is predictively most sensitive, and that a number of species including a dicot species such as Myriophyllum are needed to perform accurate risk assessments of herbicides. Received: 4 May 1996/Revised: 26 September 1996     

Investigation of Concentrations of Paddy Herbicides and Their Transformation Products in the Sakura River, Japan, and Toxicity of the Compounds to a Diatom and a Green Alga

Four paddy herbicides and their transformation products (TPs) were monitored in the Sakura River, Japan, during the rice growing seasons of 2009 and 2010. Toxicity tests to an attached diatom, Mayamaea atomus, and a green alga, Pseudokirchneriella subcapitata, were also conducted. Clomeprop propionic acid, which forms from the degrading herbicide, was detected in the river water at much higher concentrations than the parent compound (the maximum concentration of the TP and the parent compound; 0.829–0.925 μg/L and 0.039–0.073 μg/L, respectively). The toxicity of the TPs to the diatom and green alga was relatively low; the 72-h median effective concentration (EC₅₀) value > 1,470 μg/L; for each compound, the maximum concentration in the river did not exceed the EC₅₀ value.     

Ecotoxicological evaluation of cork-boiling wastewaters

Toxicity tests with Vibrio fischeri, Daphnia magna, and Lemna minor were used to evaluate acute and chronic toxicity of cork-boiling wastewaters and correlation analysis was performed with physicochemical parameters. Acute toxicity values (EC₅₀) ranged from 2.3% to 24.2% in the Microtox test and from 4.4% to 29.5% in the Daphnia test. According to these values, 78% of the samples were classified as acutely toxic to the most sensitive species (V. fischeri). Significant correlation was obtained between EC₅₀ and chemical oxygen demand, biochemical oxygen demand after 5 days, total organic carbon, tannin and lignin and total solids. No significant correlation was found between the two acute tests. The D. magna chronic test showed significant differences between all tested concentrations and the control, with an EC₅₀ of 0.32%. An EC₅₀ value of 26.0% was calculated for L. minor. For the analysis of cork-boiling wastewater toxicity and routine biomonitoring, the use of the Microtox test is suggested, to afford greater environmental protection.     

Atrazine and/or Triazine Herbicides Exposure and Cancer

ABSTRACT

An objective review of the literature was undertaken concerning atrazine and/or triazine herbicides exposure and human cancer(s). The time period covered was from 1966 through 1994. Out of ten case/control studies published, six dealing with atrazine, none indicated any statistically significant association between atrazine and cancer. Two studies indicated marginally significant associations between triazines and cancer (OR = 1.6, 95% CI = 1.0-2.6 and OR = 2.7, 90% CI = 1.0-6.9). A number of studies concerned non-Hodgkin's lymphoma, with odds ratios for atrazine or triazine exposure ranging from 1.1 to 2.2. Although positive, these were not statistically significant. At this point in time, causal criteria are not satisfied for atrazine and/or triazine(s) exposure and this malignancy. The methodologies of the published studies are critiqued; herbicide exposure assessment is frequently the weakest link. Several epide-miologic studies concerning atrazine or triazines exposure and cancer are currently underway. Such research should be focused on reproductive system cancers, lymphomas, and leukemias.     

Effect of Glyphosate on Growth of Four Freshwater Species of Phytoplankton: A Microplate Bioassay

The acute toxicity of glyphosate herbicide was tested on the four species of freshwater phytoplankton, Scenedesmus acutus, Scenedesmus subspicatus, Chlorella vulgaris and Chlorella saccharophila. Herbicide concentrations eliciting a 50% growth reduction over 72 h (EC₅₀) ranged from 24.5 to 41.7 mg L⁻¹, whilst a 10% growth inhibition is achieved by herbicide concentrations ranging from 1.6 to 3.0 mg L⁻¹, difficult to find neither in paddy fields (it is not used in rice) nor in the lake of the Albufera Natural Park. Chorella species are less sensitive to the herbicide than Scenedesmus species. It can be concluded that glyphosate has a low potential risk for the tested organisms.     

Physiological aspects of atrazine degradation by higher marine fungi

The influence of glucose and NH₄NO₃ on the degradation of the herbicide atrazine was studied with the marine fungusPericonia prolifica Anastasiou. The bioaccumulation of¹⁴C-atrazine by fungal cultures was substantially increased at increased concentrations of glucose. Overall, 34.1% of the initial atrazine concentration was removed from the culture filtrate of the cultures grown in 0.5% (w/v) glucose and 0.007% (w/v) NH₄NO₃, and 40.4% of the initial atrazine concentration was removed when the same media contained 0.08% (w/v) NH₄NO₃. The majority of internalized radioactivity from both sets of cultures could be extracted from the mycelia as undegraded atrazine. However, examination of both the culture filtrates and mycelia of cultures grown under 0.5% (w/v) glucose and 0.08% (w/v) NH₄NO₃ revealed the presence of both dealkylated and dechlorinated hydrolysis products of atrazine. The fungal cultures, compared with uninoculated controls, showed a 5-fold increase in 2-chloro-4-ethylamino-6-amino-striazine (deisopropylatrazine), a 1.9-fold increase in 2-hydroxy-4-ethylamino-6-isopropylamino-s-triazine (hydroxyatrazine), and a 1.5-fold increase in other metabolites not extracted into ethyl acetate, suggesting two separate degradation pathways caused by a combination of metabolic and physicochemical interactions. Although mineralization of [ring-¹⁴C] atrazine did not occur under the conditions employed, considerable radioactivity was found in an unextractable form associated with cell fragments ofPericonia cultures indicating further metabolism of the initial degradation products.     

Tolerance of Oscillatoria limnetica Lemmermann to Atrazine in Natural Phytoplankton Populations and in Pure Culture: Influence of Season and Temperature

The responses of algae to herbicides depend on the sensitivity of each species, but competition within algal communities may be an important regulator of the effects of herbicides on aquatic systems. The impact of herbicides on algae also depends on abiotic factors like nutrients, light, and temperature. We examined the tolerance of the alga Oscillatoria limnetica Lemmermann to the photosystem II inhibitor herbicide atrazine under different culture conditions to assess those interactions between herbicides and biotic and abiotic factors. The density of the cyanobacterium O. limnetica was determined in natural phytoplanktonic assemblages and in unialgal cultures in medium containing 10 μg/L atrazine. Experiments (total of 13) were conducted in spring and early and late summer, during which the effect of atrazine varied in nature and intensity. The growth of the cyanobacterium was always inhibited in cold experiments, whereas it was stimulated in warm experiments within the natural phytoplankton assemblage, but unaffected in pure culture. Laboratory experiments with unialgal culture showed that the sensitivity to atrazine increased as the temperature decreased. Phytoplankton community structure, interactions between species, and environmental parameters (e.g., temperature) are important factors controlling the responses of cyanobacteria to the herbicide. These interactions between sensitivity to herbicides and environmental factors may reduce or emphasize the effects of pollution in aquatic systems. Thus, the ecotoxicological relevance of herbicides in aquatic systems is quite complex and cannot be assessed by single-species short-term laboratory toxicological tests. Received: 29 January 1999/Accepted: 7 June 1999     

The influence of solvent type on solvent-pesticide interactions in bioassays

The effect of solvent type on solvent-pesticide interactions was examined by interacting the fungicide captan with the solvents acetone, ethanol, methanol, hexane, dimethyl sulfoxide (DMSO), andN,N-dimethylformamide (DMF), using growth of the fungiPythium ultimum, Sclerotinia homeocarpa, andPestalotia sp. as a toxicity criterion. DMF, ethanol, and methanol were generally the most toxic solvents tested, yielding EC₅₀ values from 0.51 to 2.29% (v/v). The least toxic solvent was hexane, with EC₅₀ values up to 36.60% (v/v). Acetone and DMSO evidenced median toxicity, yielding EC₅₀ values of 1.99 to 12.07% (v/v). WithP. ultimum andS. homeocarpa, captan interacted synergistically with all solvents tested except hexane, with the actual solvent concentration at which synergism occurred being dependent upon the level of captan. Hexane interacted additively with 2.5 ppm captan towardsS. homecarpa, antagonistically with 5.0 ppm captan towardsP. ultimum and synergistically with captan in all other combinations tested. WithPestalotia sp., captan interacted antagonistically with acetone, ethanol, and methanol, and synergistically with hexane, DMSO, and DMF. Captan was more toxic towardsP. ultimum when dissolved in DMSO, and less toxic in the presence of hexane and DMF. WithS. homeocarpa, captan was more toxic with ethanol and DMSO, and less toxic when dissolved in acetone, methanol, and hexane. DMSO and hexane elicited less toxicity from captan when tested towardsPestalotia sp., while acetone, ethanol, and methanol elicited the greatest toxicity.     

Effect of urea on degradation of terbuthylazine in soil

Pesticide and nitrate contamination of soil and groundwater from agriculture is an environmental and public health concern worldwide. The herbicide terbuthylazine (CBET) has replaced atrazine in Italy and in many other countries because the use of the latter has been banned because of its adverse environmental impacts. Unlike atrazine, knowledge about the fate of CBET in soil is still not extensive, especially regarding its transformation products, but recent monitoring data show its occurrence and that of its main metabolite, desethyl-terbuthylazine (CBAT), in groundwater above the limit of 0.1 microg/L established by European Union Directive and Italian legislation. The objective of this work was to investigate if the presence of the fertilizer urea affects CBET degradation in the soil. Laboratory CBET degradation experiments in the presence/absence of urea were performed with microbiologically active soil and sterilized soil. Terbuthylazine degradation rates under the different experimental conditions were assessed, and the formation, degradation, and transformation of the metabolite CBAT were also studied. Terbuthylazine degradation was affected by the presence of urea, in terms both of a higher disappearance time of 50% of the initial concentration and of a lower amount of CBAT formed. These findings have practical implications for the real-life assessment of the environmental fate of triazine herbicides in agricultural areas since these herbicides are frequently applied to soils receiving ureic fertilizers.     

Comparision of Atrazine and Metolachlor Affinity for Bermudagrass (Cynodon dactylon L.) and Two Soils

Given that bermudagrass is being used as one of the grasses of choice in grass filter strip plantings as an acceptable grass to reduce off-target losses of herbicides, laboratory experiments were conducted to determine and compare the relative affinity of bermudagrass, a Weswood soil, and a Houston Black soil for atrazine (6-chloro-N-ethyl-N-isopropyl-1,3,5-triazine-2,4-diamine) and metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)–N-(2-methoxy-1-methyethyl) acetamide). Experiments were also conducted to determine if the presence of one herbicide affects the relative affinity of the other compound to these sorbents. The experiments were carried out using radiolabeled atrazine and metolachlor. Results were reported in disintegrations min⁻¹ (dpms) and converted to K _d to determine and compare relative affinity. Both K _d values for relative affinity of atrazine (86.2) and metolachlor (131.5) to bermudagrass were significantly greater than those of the two soils, Weswood (atrazine, 20.0 and metolachlor, 28.4) and Houston Black (atrazine, 35.8 and metolachlor, 33.5). The two compounds were also mixed together to mimic the common practice of applying atrazine and metolachlor simultaneously as a tank mix. Relative affinity of atrazine to any of the sorbents was not affected by the presence of metolachlor. Similarly, when comparing the affinity of metolachlor alone to that of metolachlor with atrazine present in the solution, no significant differences were observed for bermudagrass or the Weswood soil. However, on the Houston Black soil, the presence of atrazine significantly increased the soil's affinity for metolachlor. Received: 15 October 2001/Accepted: 5 April 2002     

The Effect of Tributyltin-Oxide on Earthworms, Springtails, and Plants in Artificial and Natural Soils

Chemical bioavailability in Organisation for Economic Co-operation and Development (OECD) artificial soil can contrast with bioavailability in natural soils and produce ecotoxicologic benchmarks that are not representative of species’ exposure conditions in the field. Initially, reproduction and growth of earthworm and Collembolan species, and early seedling growth of a dicotyledonous plant species, in nine natural soils (with a wide range of physicochemical properties) and in OECD soil were evaluated. Soils that supported reproduction and growth of the test species were then used to investigate the toxicity of tributyltin-oxide (TBT-O). Natural soils caused greater toxicity of TBT-O to earthworms (EC₅₀ values varied from 0.5 to 4.7 mg/kg soil dry weight [dw]) compared with toxicity in OECD soil (EC₅₀ = 13.4 mg/kg dw). Collembolans were less sensitive to TBT-O than earthworms in natural soils, with EC₅₀ values ranging from 23.4 to 177.8 mg/kg dw. In contrast, the toxicity of TBT-O to collembolans in OECD soil (EC₅₀ = 104.0 mg/kg dw) was within the range of EC₅₀ values in natural soils. Phytotoxicity tests revealed even greater difference between the effects in natural soils (EC₅₀ values ranged from 10.7 to 189.2 mg/kg dw) and in OECD soil (EC₅₀ = 535.5 mg/kg dw) compared with results of the earthworm tests. Studies also showed that EC₅₀ values were a more robust end point compared with EC₁₀ values based on comparisons of coefficients of variation. These results show that toxicity testing should include studies with natural soils in addition to OECD soil to better reflect exposure conditions in the field.     

Teratogenic effects of amitraz, 2,4-dimethylaniline,and paraquat on developing frog (Xenopus) embryos

Developmental effects of amitraz (acaricide), its metabolite (2,4-dimethylaniline), and paraquat (herbicide) on embryos of a nontarget organism, Xenopus laevis, were investigated. Following the standard protocol of the American Society for Testing and Materials (ASTM), the experiments were carried out using native Xenopus frogs. There was a drastic increase in mortality from 24 h to 96 h for paraquat, but 2,4-dimethylaniline showed no mortality at the highest concentration tested (100 mg/L). The 96-h LC₅₀ values were 0.67, 3.27, and ≫100 mg/L for paraquat, amitraz, and 2,4-dimethylaniline, respectively. At concentrations higher than 0.2 mg/L of paraquat all the embryos were malformed, whereas growth reduction was apparent at all test concentrations (0.1–5 mg/L). The most common teratogenic effects were flexures of the notochord and stunting of growth. Edema was the most common effect of amitraz on the embryos, and 100% of the surviving embryos in 5 mg/L were edematous. The 96-h EC₅₀ (malformation) values were 1.21 (95% CI 0.48–3.03) and 0.18 (95% CI 0.16–0.20) mg/L for amitraz and paraquat, respectively. The ratio of 96-h LC₅₀ to 96-h EC₅₀ (malformation), i.e., the teratogenicity index (TI) were 2.7 and 3.72 for amitraz and paraquat, respectively, and for 2,4-dimethylaniline (TI > 5) all the embryos in 25 mg/L showed observable pigment loss and encephalomegaly. This shows that paraquat and the degradation product of amitraz, 2,4-dimethylaniline, should be classified as teratogens. Teratogenic risks of massive application of these pesticides on Kenyan farms should therefore be considered. Received: 27 June 2001/Accepted: 4 February 2002     

Mortality and LC50Values for Several Stages of the Marine CopepodTigriopus brevicornis(Müller) Exposed to the Metals Arsenic and Cadmium and the Pesticides Atrazine, Carbofuran, Dichlorvos, and Malathion

The toxicity of three insecticides (carbofuran, dichlorvos, malathion), an herbicide (atrazine), and two metals (arsenic and cadmium) to ovigerous females, copepodids, and nauplii ofTigriopus brevicorniswas determined by 96-h semistatic (or static-renewal) bioassays. Freshly prepared aqueous stock solutions of these pesticides and metals were diluted to appropriate concentrations. Mortalities were recorded and test solutions were changed completely each day up to 96 h. The rate of mortality was analyzed for linear regressions, and LC₅₀values were determined by probit analysis. LC₅₀values for ovigerousT. brevicornisfemales were 153.2 μg liter⁻¹for atrazine, 59.9 μg liter⁻¹for carbofuran, 47.9 μg liter⁻¹for cadmium, 27.5 μg liter⁻¹for arsenic, 24.3 μg liter⁻¹for malathion, and 4.6 μg liter⁻¹for dichlorvos. Comparison of the overall toxicities of these pesticides and metals indicated that dichlorvos was the most toxic substance toT. brevicornis, followed by malathion, arsenic, cadmium, carbofuran, and atrazine. Available LC₅₀data indicate that marine copepods are more sensitive to pollutants thanDaphnia magna, Acartia tonsa, andTisbe battagliai, or as sensitive as the mysidMysidopsis bahia.     

In Ovo Exposure to a Triazine Herbicide: Effects of Atrazine on Circulating Reproductive Hormones and Gonadal Histology in Young Japanese Quail

The triazine herbicide, atrazine, has come under scrutiny for its reported feminizing effects in amphibians. To date, there is little information concerning the effects of atrazine on reproduction in avian species. The current study examined the putative reproductive toxicity of atrazine after exposure in ovo. Atrazine at 504, 246, and 123 μg/kg was administered to Japanese quail eggs before incubation. The eggs were hatched and the birds raised to 14 days of age. Indices of hatchability, sex ratios, and growth were determined. Furthermore, circulating concentrations of reproductive hormones (estradiol, progesterone, and testosterone) and gonadal histology were examined. Atrazine at 504 μg/kg decreased 14-day hatchling weight by 13.1% versus controls. However, no detrimental effects on hatchability or sex ratios were observed. In female birds, atrazine at 504 μg/kg decreased ovarian weights and circulating concentrations of progesterone to 48.3% and 73.3%, respectively, versus control. However, concentrations of estradiol and testosterone did not differ from controls. In male quail, at all doses tested, atrazine had no effect on gonadal weights or circulating concentrations of estradiol, testosterone, or progesterone. Moreover, no incidences of left ovotestis formation were observed. In contrast, 10 ng/kg ethinylestradiol (a positive control) induced the formation of a left ovotestis in four of eight birds analyzed. The current results may suggest that exposure to atrazine in ovo at concentrations above ecologic relevance exerts effects on the reproductive system of young Japanese quail. However, no evidence is presented that atrazine induces feminization of the testis in male quail.