Reduction of doxorubicin-induced genotoxicity by Handroanthus impetiginosus in mouse bone marrow revealed by micronucleus assay / Redução da genotoxicidade induzida pela doxorrubicina por Handroanthus impetiginosus na medula óssea de camundongos revelada pelo ensaio do micronúcleo

Handroanthus impetiginosus has long been used in traditional medicine and various studies have determined the presence of bioactive chemical compounds and potential phytotherapeutics. In this study, the genotoxicity of the lyophilized tincture of H. impetiginosus bark (THI) was evaluated in mouse bone marrow using micronucleus assays. The interaction between THI and genotoxic effects induced by the chemotherapeutic agent, doxorubicin (DXR), was also analyzed. Experimental groups were evaluated 24 to 48 h after treatment with N-nitroso-N-ethylurea (NEU; 50 mg/kg), DXR (5 mg/kg), sodium chloride (NaCl; 150 mM), and THI (0.5-2 g/kg). Antigenotoxic assays were carried out using THI (0.5 g/kg) in combination with NEU or DXR. Analysis of the micronucleated polychromatic erythrocytes (MNPCEs) indicated no significant differences between treatment doses of THI (0.5-2 g/kg) and NaCl. Polychromatic erythrocyte (PCE) to normochromatic erythrocyte (NCE) ratios did not indicate any statistical differences between DXR and THI or NaCl, but there were differences between THI and NaCl. A significant reduction in MNPCEs and PCE/NCE ratios was observed when THI was administered in combination with DXR. This study suggested the absence of THI genotoxicity that was dose-, time-, and gender-independent and the presence of moderate systemic toxicity that was dose-independent, but time- and gender-dependent. The combination of THI and DXR also suggested antigenotoxic effects, indicating that THI reduced genotoxic effects induced by chemotherapeutic agents.(AU)

Handroanthus impetiginosus tem sido usada durante um longo período pela medicina tradicional e vários estudos têm demonstrados a presença de compostos químicos e potencial fitoterapêutico. Esta pesquisa avaliou a genotoxicidade da tintura da casca liofilizada de H. impetiginosus (THI) usando o ensaio do micronúcleo em medula óssea de camundongos. A interação entre THI e os efeitos genotóxicos induzidos pelo quimioterápico doxorrubicina (DXR) também foram analisados. Grupos experimentais foram analisados a 24-48 h após o tratamento com N-Nitroso-N-etiluréia (NEU; 50 mg/kg), DXR (5 mg/kg), NaCl (150 mM) e THI (0,5-2 g/kg). O ensaio antigenotóxico foi conduzido utilizando THI (0,5 g/kg) em combinação com NEU ou DXR. A análise de eritrócitos policromáticos micronucleados (EPCMNs) não mostrou diferenças significativas entre as doses de tratamento (0,5-2 g/kg) e NaCl. As proporções de eritrócitos policromáticos (EPC)/eritrócitos normocromáticos (ENC) não revelaram diferenças estatísticas entre DXR e THI ou NaCl, porém houve diferenças entre THI e NaCl. Uma redução significativa em EPCMNs e na razão EPC/ENC foi observada quando THI foi administrado em combinação com DXR. Essa pesquisa sugere ausência de genotoxicidade de THI, dose-, tempo- e sexo-independente, e moderada toxicidade sistêmica dose-independente, mas tempo- e sexo-dependente. A associação do THI e DXR também sugere efeitos antigenotóxicos. Por conseguinte, THI pode reduzir os efeitos genotóxicos induzidos pelo quimioterapêutico.(AU)

Analysis of various effects of abamectin on erythrocyte morphology in Japanese quails (Coturnix japonica).

Although previous studies have already confirmed the toxicological potential of abamectin (ABA) in different experimental models (from invertebrates to vertebrates), almost nothing is known about the impacts the exposure to this pesticide can cause on birds. Thus, the aim of our study is to investigate the cytotoxic effects on the erythrocytes of female Japanese quails (Coturnix japonica) exposed to low abamectin concentrations. In order to do so, three experimental groups were proposed: "control," composed of quails exposed to abamectin-free drinking water; "ABA 1% median lethal dose (LD50)," comprising birds exposed to water containing 15.5 mg a.i./L of abamectin (via commercial formulation Kraft® 36EC), and "ABA 10% LD50," composed by birds exposed to water containing 155.0 mg a.i./L of abamectin. The micronucleus test and the tests applied to other nuclear abnormalities in the peripheral blood of birds were conducted 40 days after exposure. Our study revealed significant physical abnormalities in nuclear shapes (erythrocytes with asymmetric constriction nuclei, notched nuclei, indented and moved nucleus) of those birds exposed to higher abamectin levels. When all nuclear abnormalities were tallied, a significant dose-dependent trend was noted. Therefore, our study presents initial imprints on determination of abamectin-mediated cellular toxicity in avifauna which can be instrumental in checking polluted ecosystems.

Activity of the endophytic fungi Phlebia sp. and Paecilomyces formosus in decolourisation and the reduction of reactive dyes' cytotoxicity in fish erythrocytes.

The current study investigates the potential for discolouration and degradation of Reactive Blue 19 and Reactive Black 5 textile dyes by endophytic fungi Phlebia sp. and Paecilomyces formosus as well as the potential cytotoxicity of products or by-products generated by the treatments in fish erythrocytes. It was observed at 30 days that both endophytes showed biodegradation activity with 0.1 g mL-1 of dyes. P. formosus showed highest extracellular and intracellular protein content levels after the 15th day, and Phlebia sp. stands out for production of extracellular laccase, indicating that this enzyme may be associated with the decolouration capacity. The dyes showed toxic effects in fishes at 0.01 g mL-1 concentration, resulting in the appearance of micronuclei in erythrocyte cells. When degraded dyes treated by endophytes were tested, the frequency of micronuclei reduced approximately 20%, indicating the effectiveness of these endophytic in the treatment of textile dyes with less environmental impact, thus indicating a potential for application of these fungi in bioremediation process.

Evaluation of Stage-Dependent Genotoxic Effect of Roundup® (Glyphosate) on Caiman latirostris Embryos.

The agricultural expansion over the past decades, along with the associated increase in the use of pesticides, represents a high risk for many wild species. Caiman latirostris is a South American caiman with many features that make it highly vulnerable to pesticide exposure. Considering previous finding on the genotoxicity of the glyphosate-based formulation Roundup® in this species, the aim of this study was to evaluate the possible stage-dependent effect of this compound on C. latirostris embryos through the Comet assay (CA), micronuclei (MN), and nuclear abnormalities (NA) tests. Caiman eggs were exposed to three effective concentrations of Roundup® (750, 1250, 1750 µg/egg) in three different stages of the incubation period (total duration 70 ± 3 days at 31 ± 2 °C) of approximately 23 days each. A statistically significant difference in DNA damage determined by the CA was found between groups exposed to different concentrations of RU (p < 0.05) and the negative control, but no difference was observed among the three stages of exposure within any treatment (p > 0.05). There was no differences in the MN or NA frequencies between the different groups and the negative control (p > 0.05), nor among the different stages within each treatment. The results obtained in this study indicate that RU produce DNA damage on C. latirostris embryos independently of the developmental stage where the exposure occurs, implying an important risk for the species during all its period of development, when pesticide application is at maximum rate.

Assessment of genotoxic, mutagenic, and recombinogenic potential of water resources in the Paranaíba River basin of Brazil: A case study.

Exposure to certain pollutants induces a series of alterations in deoxyribonucleic acid (DNA) that may result in genotoxic/mutagenic effects in exposed individuals. The present study aimed to monitor genotoxic, mutagenic, and recombinogenic potential and consequently water quality in two streams in the Paranaíba River basin in the state of Minas Gerais, Brazil, using two bioindicator fish (Rhamdia quelen and Geophagus brasiliensis). The micronucleus (MN) test and somatic recombination and mutation test (SMART) were employed to assess DNA damage. The water quality index (WQI) at the reference site control (S1) due to its proximity to the river source was compared to Córrego do Óleo (S2) with respect to chemical parameter levels of biochemical oxygen demand (BOD), dissolved-oxygen rates (DO), and total solid and fecal coliform counts. These chemical parameters were above the permitted limits at Córrego do Óleo (S2). At a third site, Córrego Liso (S3), a poor WQI was detected, attributed to the influence of domestic and industrial activities where BOD, DO, total solid, fecal coliform, total phosphorus, and turbidity rates exceeded premissible limits. The MN frequencies and the numbers of MN per cell (CMN) at sites S2 and S3 were significantly higher than those at S1 in both species. It is of interest that the increased frequency of MN was similar to the positive control cyclophosphamide only at S3, suggesting that the effects of water contaminants were most severe at this site. At sites assessed (S2 and S3), there was a significant rise in somatic mutation and recombination in the wings of Drosophila melanogaster, indicating the presence of trace elements, mainly lead (Pb) and cadmium (Cd), in the effluents in the Paranaíba River basin sites.

Genotoxic and mutagenic evaluation of water samples from a river under the influence of different anthropogenic activities.

Pollution of aquatic ecosystems is associated with the discharge of mostly industrial and urban effluents, which may cause loss of biodiversity and damage to public health. This study aims to evaluate the toxicity and mutagenicity of water samples collected in the Corrente River, a major waterway in the river basin district of Pedro II, Piauí (Brazil). This river is exposed to intense anthropogenic influence from urban, automotive mechanical and family farm waste, and it is used as the main source of water supply by the population. Water samples were collected during the rainy and dry seasons, at four sites in the Corrente River, and evaluated by physicochemical, microbiological and inorganic elements analyses. The samples were evaluated for mutagenicity using the Allium cepa test (toxicity, chromosomal aberration and micronucleus tests) and fish (Tilapia rendalli and Hoplias malabaricus). The physicochemical, microbiological and inorganic results show a large contribution to the pollution loads at collection points in the town of Pedro II, demonstrating the influence of urban pollution. The Al, Si, Ti, Cr, Ni and Cu contents were determined by PIXE. These same Corrente River water samples demonstrated mutagenic effect for A. cepa and fish, as well as toxicity in the A. cepa test. The observations of mutagenic effect may suggest that the complex mixture of agents is comprised of both clastogenic and aneugenic agents. This study also showed the need for constant monitoring in places with environmental degradation caused by urban sewage discharges.

Assessing genotoxic effects in fish from a marine protected area influenced by former mining activities and other stressors.

The goal of the current study was to evaluate different genotoxicity tools in order to assess a marine protected area (MPA) affected by former mining activities and urban settlements. A catfish (Cathorops spixii) was analyzed for genotoxic effects at the (i) molecular and at the (ii) chromosomal levels. Through factor analysis, genotoxicity was found to be linked to levels of metals bioaccumulated and PAH metabolites in the bile. Micronucleus and nuclear alteration were less vulnerable to the effects of confounding factors in mildly contaminated areas since they were more frequently associated with bioaccumulated metals than the DNA analysis. The different genotoxicity responses allowed for the identification of sources of pollution in the MPA. This approach was important for detecting environmental risks related to genotoxic contaminants in a mildly contaminated MPA.

Avaliação da mutagenicidade do indoxacarbe em ratos e gatos / Mutagenicity assessment of indoxacarb in rats and cats

Background: Pesticides are substances used for pest control. Due to their persistence in the environment, they can induce toxicity in humans and animals. Indoxacarb is an oxadiazine insecticide that acts against insects of the order Lepidoptera. Choice of rats and cats used in this study is based on factors such as these animals have a high count of micronucleated polychromatic erythrocytes and the product is intended for use in cats. Limited data in literature pertaining to the mutagenic effects of this product motivated this study. The aim of this study was to evaluate the effect of the micronucleus test on the mutagenicity of indoxacarb when administered in one and tenfold therapeutic doses in rats and cats.Materials, Methods & Results: Forty male Wistar rats aged 70 days and weighing 280 ± 10 g and 20 mixed breed male and female adult cats weighing 4 ± 0.2 kg were selected. These animals were obtained from the central animal facility and cattery, respectively, of the university of origin. Rats were reared in individual cages with a controlled temperature of 22°C ± 2°C, humidity of 55% ± 5% and 12-h light–dark cycle. Cats were reared in individual stalls with water and food ad libitum. Animals were randomly distributed into four groups comprising 10 rats and 5 cats in respective groups: negative control group, which received 0.9% sodium chloride solution as a single topical administration; positive control group, which received 50 mg/kg cyclophosphamide as a single intra-peritoneal (rats) or intravenous injection (cats); indoxacarb group, which received indoxacarb as a single topical dose according to the manufacturer’s recommendations; and high dose indoxacarb group, which also received indoxacarb in a single topical dose, but at a tenfold concentration. Rats were evaluated 24 h after indoxacarb administration. After euthanasia, rat femurs were obtained and their medullary canals were washed using fetal bovine serum.[...]

Avaliação da mutagenicidade do indoxacarbe em ratos e gatos / Mutagenicity assessment of indoxacarb in rats and cats

Background: Pesticides are substances used for pest control. Due to their persistence in the environment, they can induce toxicity in humans and animals. Indoxacarb is an oxadiazine insecticide that acts against insects of the order Lepidoptera. Choice of rats and cats used in this study is based on factors such as these animals have a high count of micronucleated polychromatic erythrocytes and the product is intended for use in cats. Limited data in literature pertaining to the mutagenic effects of this product motivated this study. The aim of this study was to evaluate the effect of the micronucleus test on the mutagenicity of indoxacarb when administered in one and tenfold therapeutic doses in rats and cats.Materials, Methods & Results: Forty male Wistar rats aged 70 days and weighing 280 ± 10 g and 20 mixed breed male and female adult cats weighing 4 ± 0.2 kg were selected. These animals were obtained from the central animal facility and cattery, respectively, of the university of origin. Rats were reared in individual cages with a controlled temperature of 22°C ± 2°C, humidity of 55% ± 5% and 12-h light–dark cycle. Cats were reared in individual stalls with water and food ad libitum. Animals were randomly distributed into four groups comprising 10 rats and 5 cats in respective groups: negative control group, which received 0.9% sodium chloride solution as a single topical administration; positive control group, which received 50 mg/kg cyclophosphamide as a single intra-peritoneal (rats) or intravenous injection (cats); indoxacarb group, which received indoxacarb as a single topical dose according to the manufacturers recommendations; and high dose indoxacarb group, which also received indoxacarb in a single topical dose, but at a tenfold concentration. Rats were evaluated 24 h after indoxacarb administration. After euthanasia, rat femurs were obtained and their medullary canals were washed using fetal bovine serum.[...](AU)

Acute copper toxicity in juvenile fat snook Centropomus parallelus (Teleostei: Centropomidae) in sea water

Three experiments were designed to assess the accumulation and acute toxicity of copper (Cu) in juvenile fat snook Centropomus parallelus. The first experiment was performed to determine the 96-h lethal concentration (LC50) of Cu. The second experiment was designed to assess the effects of sublethal concentrations of Cu (0.47 and 0.94 mg/L), while the third one allowed us to test the recovery capacity of fish exposed to the sublethal concentrations Cu and kept in sea water without Cu addition. The LC50 value for Cu was found to be 1.88 mg/L Cu. Fish exposed to the sublethal concentrations of Cu showed a significant accumulation of Cu in gills at 96 h respect to the control ones (0.43 µg/g Cu). No significant difference was observed in the accumulation of Cu in gills between fish exposed to 0.47 mg/L (1.09 µg/g Cu) and 0.94 mg/L (1.26 µg/g Cu). Exposure (24 and 96 h) to the sublethal concentrations of Cu tested induced DNA damage in the erythrocytes. The results show that acute exposure to sublethal concentrations induces Cu accumulation and DNA damage in fish, these effects being recovered after 240 h in sea water without Cu addition.

Três experimentos foram realizados para avaliar o acúmulo e toxicidade aguda do cobre (Cu) em juvenis de robalo-peva Centropomus parallelus. O primeiro experimento foi realizado para determinar a concentração letal (96h-CL50) de Cu. O segundo experimento foi realizado para avaliar os efeitos de concentrações subletais de Cu (0,47 e 0,94 mg/L), enquanto o terceiro permitiu testar a capacidade de recuperação dos peixes expostos a concentrações subletais do Cu e posteriormente mantidos em água do mar sem acréscimo de Cu. O valor de LC50 encontrado para o Cu foi de 1,88 mg/L. Os peixes expostos as concentrações subletais de Cu mostraram um acúmulo significativo nas brânquias em relação ao controle em 96 h de exposição (0,43 µg/g Cu). Nenhuma diferença significativa foi observada entre os peixes expostos a 0,47 mg/L de Cu (1,09 µg/g) e 0,94 mg/L de Cu (1,26 µg/g). A exposição (24 e 96 h) para as concentrações subletais de Cu induziram danos no DNA. Os resultados mostram que a exposição aguda a concentrações subletais induz o acúmulo de Cu e danos ao DNA nas brânquias dos peixes, onde estes efeitos são recuperados após 240 h em água do mar sem adição de Cu.

Acute copper toxicity in juvenile fat snook Centropomus parallelus (Teleostei: Centropomidae) in sea water

Three experiments were designed to assess the accumulation and acute toxicity of copper (Cu) in juvenile fat snook Centropomus parallelus. The first experiment was performed to determine the 96-h lethal concentration (LC50) of Cu. The second experiment was designed to assess the effects of sublethal concentrations of Cu (0.47 and 0.94 mg/L), while the third one allowed us to test the recovery capacity of fish exposed to the sublethal concentrations Cu and kept in sea water without Cu addition. The LC50 value for Cu was found to be 1.88 mg/L Cu. Fish exposed to the sublethal concentrations of Cu showed a significant accumulation of Cu in gills at 96 h respect to the control ones (0.43 µg/g Cu). No significant difference was observed in the accumulation of Cu in gills between fish exposed to 0.47 mg/L (1.09 µg/g Cu) and 0.94 mg/L (1.26 µg/g Cu). Exposure (24 and 96 h) to the sublethal concentrations of Cu tested induced DNA damage in the erythrocytes. The results show that acute exposure to sublethal concentrations induces Cu accumulation and DNA damage in fish, these effects being recovered after 240 h in sea water without Cu addition.(AU)

Três experimentos foram realizados para avaliar o acúmulo e toxicidade aguda do cobre (Cu) em juvenis de robalo-peva Centropomus parallelus. O primeiro experimento foi realizado para determinar a concentração letal (96h-CL50) de Cu. O segundo experimento foi realizado para avaliar os efeitos de concentrações subletais de Cu (0,47 e 0,94 mg/L), enquanto o terceiro permitiu testar a capacidade de recuperação dos peixes expostos a concentrações subletais do Cu e posteriormente mantidos em água do mar sem acréscimo de Cu. O valor de LC50 encontrado para o Cu foi de 1,88 mg/L. Os peixes expostos as concentrações subletais de Cu mostraram um acúmulo significativo nas brânquias em relação ao controle em 96 h de exposição (0,43 µg/g Cu). Nenhuma diferença significativa foi observada entre os peixes expostos a 0,47 mg/L de Cu (1,09 µg/g) e 0,94 mg/L de Cu (1,26 µg/g). A exposição (24 e 96 h) para as concentrações subletais de Cu induziram danos no DNA. Os resultados mostram que a exposição aguda a concentrações subletais induz o acúmulo de Cu e danos ao DNA nas brânquias dos peixes, onde estes efeitos são recuperados após 240 h em água do mar sem adição de Cu.(AU)

Baseline micronuclei and nuclear abnormalities frequencies in native fishes from the Paraná River (Argentina).

This work aims to establish baseline frequencies of micronuclei (MN) and nuclear abnormalities (NA) in native fish species collected in situ from the Paraná River. For this purpose, the micronucleus test was applied in peripheral blood erythrocytes from specimens obtained from samplings collected at two localities (Posadas and Candelaria, Misiones, Argentina) during the period 2007-2010. The results were statistically analyzed using the Kruskal Wallis test. Data from nine fish species were obtained, among which Steindachnerina brevipinna (Characiformes) revealed the highest baseline frequency of MN and NA, showing statistically significant differences with regard to the other analyzed species. These results are the first report of baseline MN and NA frequencies for native fish species studied and could be useful for future comparisons with data of fishes belonging to other environments.

Baseline micronuclei and nuclear abnormalities frequencies in native fishes from the Paraná River (Argentina) / Frequências basais de micronúcleos e anormalidades nucleares em peixes nativos do Rio Paraná (Argentina)

This work aims to establish baseline frequencies of micronuclei (MN) and nuclear abnormalities (NA) in native fish species collected in situ from the Paraná River. For this purpose, the micronucleus test was applied in peripheral blood erythrocytes from specimens obtained from samplings collected at two localities (Posadas and Candelaria, Misiones, Argentina) during the period 2007-2010. The results were statistically analyzed using the Kruskal Wallis test. Data from nine fish species were obtained, among which Steindachnerina brevipinna (Characiformes) revealed the highest baseline frequency of MN and NA, showing statistically significant differences with regard to the other analyzed species. These results are the first report of baseline MN and NA frequencies for native fish species studied and could be useful for future comparisons with data of fishes belonging to other environments.

O presente trabalho tem como objetivo estabelecer frequências basais de micronúcleos (MN) e anormalidades nucleares (AN) em espécies nativas de peixes obtidas in situ no Rio Paraná. Para este efeito, o teste do micronúcleo foi aplicado em eritrócitos de sangue periférico de espécimes provenientes de amostragens efetuadas em duas localidades (Posadas e Candelaria, Misiones, Argentina) durante o período 2007-2010. Os resultados foram analisados estatisticamente empregando o teste de Kruskal Wallis. Foram coletados dados de nove espécies e dentre estas Steindachnerina brevipinna (Characiformes) revelou a maior frequência basal de MN e AN, mostrando diferenças estatisticamente significativas com respeito às outras espécies analisadas. Estes resultados são o primeiro relatório de frequências basais de MN e AN para espécies nativas de peixes estudadas e poderiam ser úteis para futuras comparações com dados de peixes pertencentes a outros ambientes.

Baseline micronuclei and nuclear abnormalities frequencies in native fishes from the Paraná River (Argentina) / Frequências basais de micronúcleos e anormalidades nucleares em peixes nativos do Rio Paraná (Argentina)

This work aims to establish baseline frequencies of micronuclei (MN) and nuclear abnormalities (NA) in native fish species collected in situ from the Paraná River. For this purpose, the micronucleus test was applied in peripheral blood erythrocytes from specimens obtained from samplings collected at two localities (Posadas and Candelaria, Misiones, Argentina) during the period 2007-2010. The results were statistically analyzed using the Kruskal Wallis test. Data from nine fish species were obtained, among which Steindachnerina brevipinna (Characiformes) revealed the highest baseline frequency of MN and NA, showing statistically significant differences with regard to the other analyzed species. These results are the first report of baseline MN and NA frequencies for native fish species studied and could be useful for future comparisons with data of fishes belonging to other environments.(AU)

O presente trabalho tem como objetivo estabelecer frequências basais de micronúcleos (MN) e anormalidades nucleares (AN) em espécies nativas de peixes obtidas in situ no Rio Paraná. Para este efeito, o teste do micronúcleo foi aplicado em eritrócitos de sangue periférico de espécimes provenientes de amostragens efetuadas em duas localidades (Posadas e Candelaria, Misiones, Argentina) durante o período 2007-2010. Os resultados foram analisados estatisticamente empregando o teste de Kruskal Wallis. Foram coletados dados de nove espécies e dentre estas Steindachnerina brevipinna (Characiformes) revelou a maior frequência basal de MN e AN, mostrando diferenças estatisticamente significativas com respeito às outras espécies analisadas. Estes resultados são o primeiro relatório de frequências basais de MN e AN para espécies nativas de peixes estudadas e poderiam ser úteis para futuras comparações com dados de peixes pertencentes a outros ambientes.(AU)

Biomarkers of exposure and effect in the Brazilian flounder Paralichthys orbignyanus (Teleostei: Paralichthyidae) from the Patos Lagoon estuary (Southern Brazil).

Biomarkers of exposure (liver metallothionein-like proteins content and catalase and glutathione S-transferase activities) and effect (liver lipoperoxidation and blood cell DNA damage) of contaminants were analyzed in the Brazilian flounder Paralichthys orbignyanus from the Patos Lagoon estuary (Southern Brazil). Flounders were collected for a year in two sites: "Coroa do Boi" (polluted site) and "Saco do Justino" (non-polluted site). Results indicated that micronucleated cells frequency was the best biomarker to distinguish flounders from the two sites. Taken together, data from DNA damage analyses (micronucleus test and comet assay) indicated that flounders from the non-polluted site efficiently repaired the DNA breaks, contrary to those from the polluted site, which probably had their DNA repair system inhibited or exhausted. Furthermore, data from enzyme activities (catalase and GST) and lipid peroxidation indicated that flounders from the polluted site were under oxidative stress in summer and autumn.

Micronucleus test in fish from a pampasic pond (Argentina): an estimation of the presence of genotoxic compounds.

The Los Padres pond is one of the commonly shallow, polymictic lakes from the so-called depressed Pampa (Argentina). Its watershed includes one affluent, named Los Padres creek, which flows through horticultural lands wherein great amounts of pesticides are applied. Opposite to this stream, the pond drains into La Tapera creek that is the effluent running toward the sea. Many studies have confirmed the capacity of various pesticides to induce genetic damage. The use of micronucleus (MN) tests in fish has enabled us to detect the presence of contaminants in the lakewater and to evaluate theirgenotoxic effects. For this purpose, water samples were collected during April, August, and December 1999 from both creeks characterized by different environmental conditions. In the laboratory, specimens oftetras Cheirodon interruptus (Pisces, Characidae) were reared in water samples from the two creeks. Control fish were kept in drinking water. Fifteen individuals from each experimental group were sacrificed after 24-, 48-, and 72-hour exposure intervals. Micronucleus frequency in fish erythrocytes was determined, and the Kruskal-Wallis test for statistic analysis was used. We made the following observations: (1) Highly significant differences occurred in MN frequency between the control group and the samples from both creeks. (2) An increase in MN frequency was evident in specimens sampled from the affluent input during the month of December. These results allowed us to conclude that the increase in MN frequency observed in fish belonging to both sampling sites would indicate the existence of genotoxic compounds in the Los Padres pond. The high MN frequency in fish collected near Los Padres creek inlet might be related to the polluted load transported by the affluent and discharged into the lake's surface waters. Future work would allow us to develop efficient methods for predicting the presence of genotoxic contaminants. It would be possible then to propose strategies for regulating and decreasing the sources of pollution that affect human health.