Assessment of chronic effects of tebuconazole on survival, reproduction and growth of Daphnia magna after different exposure times.

The effect of the fungicide tebuconazole (0.41, 0.52, 0.71 and 1.14mg/L) on survival, reproduction and growth of Daphnia magna organisms was monitored using 14 and 21 days exposure tests. A third experiment was performed by exposing D. magna to the fungicide for 14 days followed by 7 days of recovery (14+7). In order to test fungicide effects on D. magna, parameters as survival, mean whole body length, mean total number of neonates per female, mean number of broods per female, mean brood size per female, time to first brood/reproduction and intrinsic rate of natural increase (r) were used. Reproduction was seriously affected by tebuconazole. All tebuconazole concentrations tested affected the number of broods per female and day to first brood. At 14-days test, number of neonates per female and body size decreased by concentrations of tebuconazole higher than 0.52mg/L, whereas at 21-days test both parameters were affected at all the concentrations tested. Survival of the daphnids after 14 days fungicide exposure did not exhibited differences among experimental and control groups. In this experiment r value was reduced (in a 22%) when animals were exposed to concentrations of 0.71mg/L and 1.14mg/L. Survival of daphnids exposed during 21 days to 1.14mg/L declined, and the intrinsic rate of natural increase (r) decreased in a 30 % for tebuconazole concentrations higher than 0.41mg/L. Longevity of daphnids pre-exposed to tebuconazole for 14 days and 7 days in clean water did not show differences from control values and all of them survived the 21 days of the test. However, after 7 days in fungicide free medium animals were unable to restore control values for reproductive parameters and length. The maximum acceptable toxicant concentration (MATC) was calculated using the r values as parameter of evaluation. MATC estimations were 0.61mg/L and 0.46mg/L for 14 and 21 days, respectively. Results showed that the number of neonates per female was the highest sensitive parameter to the effects of tebuconazole on D. magna. On the other hand, a recovery period of 7 days in a free toxicant medium would not be longer enough to reestablish normal reproduction parameters in pre-exposed tebuconazole daphnids.

Short-term exposure to sublethal tebuconazole induces physiological impairment in male zebrafish (Danio rerio).

The aim of the present study was to assess the physiological response of male zebrafish Danio rerio to the fungicide tebuconazole and recovery in fungicide-free water. Acute toxicity tests were carried out and the median lethal concentration (LC(50)) from 24 to 96 h was calculated. The fish were exposed to a sublethal fungicide concentration of 230 microg/L for 7 or 14 days and allowed to recover for 7 or 14 more days, respectively. Whole-body levels of vitellogenins, triglycerides, cholesterol, glucose, lactate and proteins as well as the activities gamma-glutamil transpeptidase (gamma-GT), alanin aminotransferase (AlAT), alkaline phosphatase (AP) and lactate dehydrogenase (LDH) were assayed; corpulence factor (k) was also calculated. Fish exhibited significant increase of vitellogenins (Vtg), which continued to increase after 14 days of recovery. Levels of glucose, lactate, cholesterol and triglycerides increased after 7 and 14 days of exposure. Finally, cholesterol and glucose recovered after 14 days of recovery whereas triglycerides and lactate continued to be elevated. Proteins and k remained unaltered the entire experiments. AAT, AlAT and AP enhanced during exposure and did not recover at the end (except AlAT). A longer recovery period should be necessary to re-establish fish physiology. These results alert about the multiple disruptive physiological actions that tebuconazole may have on fish.

Biochemical stress response in tetradifon exposed Daphnia magna and its relationship to individual growth and reproduction.

Environmental risk assessment of chemicals toxicity requires the use of costly and labor-intensive chronic data and short-term tests provide additional information. Energy budget is used by the animals for their growth, reproduction, and metabolism and it is reduced in case of toxic stress. Tetradifon acaricide is frequently used in the European Mediterranean region and it is implicated in aquatic environmental pollution. Previous studies showed that the EC(50)-24 h of tetradifon on Daphnia magna was 8.92 mg/L. Based on that, D. magna were exposed to sublethal tetradifon concentrations of 0.10, 0.18, 0.22 and 0.44 mg/L for five days in order to investigate their effect on intermediate metabolism. Caloric content was determined as biomarker of tetradifon toxicity. Results were analyzed using one-way analysis of variance (ANOVA) and Duncan's significant difference test was used to find differences between groups (alpha was set at p=0.05). Daphnids energy content decreased as tetradifon concentration increased. At 120-h caloric content was depleted >51% at pesticide concentrations of 0.18 mg/L and higher. In order to determine a possible link between the 5-d test and the 21-d chronic test, animals under short-term test were exposed to the same pesticide concentrations known to cause adverse effects on reproduction, growth and survival. Results from the present study indicated a good correlation between the proposed 5-day test and daphnid energy budget. Comparison between both, caloric content results and the chronic effect values obtained using life-table studies, suggested a good fit between them. These studies can be used as earlier, predictive and useful tests with comparable results to the classic chronic ones. Our results indicate that caution must be done about the use of tetradifon in the aquatic environment.

Disturbances in energy metabolism of Daphnia magna after exposure to tebuconazole.

This study was conducted to investigate the change of some biochemical parameters in the aquatic invertebrate Daphnia magna following exposure to the fungicide tebuconazole and to determine the most sensitive biomarker among the ones tested in this species. Four biochemical biomarkers (protein, glycogen, lipids and caloric content) were correlated with feeding behaviour studies of D. magna after fungicide exposure. Juveniles of D. magna were exposed to four sublethal concentrations of tebuconazole (0.41, 0.52, 0.71 and 1.14 mgL(-1)) for 5d. Daphnid samples were taken from each test and control group at 24, 48, 72, 96 and 120 h after the start of the experiment. Tebuconazole EC(50) values were calculated on D. magna in our laboratory as 56.83 and 40.10 mgL(-1) at 24 and 48 h, respectively. Results showed that daphnid energy content decreased as tebuconazole concentration increased, especially after 96-120 h of exposure to 0.52 mgL(-1) and higher fungicide concentrations. The data suggest that tebuconazole is moderately toxic to D. magna but also that it seriously impairs the metabolic functions, resulting in alterations in biochemical constituents. In the D. magna feeding study, algae feeding rates were inhibited after fungicide exposure. Such findings indicate the importance of feeding studies in laboratory toxicity test as well as their relationship with others studies. The results emphasize the importance of considering different kind of biomarkers to identify and evaluate the biological effect of a fungicide in the aquatic environment. Although the biochemical biomarkers used resulted good indicators of tebuconazole toxicity, feeding rates in D. magna decreased after only 5h exposure to the fungicide resulting in the most sensitive parameter of daphnid fungicide exposure.

Acute, chronic and sublethal effects of the herbicide propanil on Daphnia magna.

Acute and chronic toxicity tests with propanil were conducted on Daphnia magna. The 24 and 48 h LC50 were 43.74 and 5.01 mg/l respectively. Chronic toxicity tests were carried out using sublethal propanil concentrations (0.07, 0.10, 0.21 and 0.55 mg/l) during 21 days. The effect of propanil on survival, reproduction and growth of D. magna organisms was monitored. The parameters used to evaluate herbicide effect on reproduction were: mean total young ones per female, mean brood size, time to first reproduction, mean number broods per female and intrinsic rate of natural increase (r). Survival and growth (body length) were also determined after 21 days of exposure to the herbicide. Reproduction was significantly reduced when propanil concentration increased in the medium. The intrinsic rate of natural increase (r) decreased with increasing concentrations of propanil especially in those animals exposed to 0.55 mg/l. However, growth as well as survival of the exposed organisms only decreased in daphnids exposed to the highest propanil concentration tested. The maximum acceptable toxicant concentration (MATC) was calculated for D. magna exposed to the herbicide using as parameter of evaluation the intrinsic rate of natural increase (r). The interpolation of these results gave MATC values of 0.08 mg/l herbicide. We have derived the EC50 values for some selected parameters on D. magna exposed to propanil. EC50 values indicated that reproductive parameters were very sensitive of the effect of propanil on daphnids. Finally, the daphnids were exposed to the same sublethal herbicide concentrations as in the chronic study and the effect of the toxicant on filtration and ingestion rates was determined. Feeding rates of D. magna declined with increasing propanil concentrations. The effective propanil concentrations at which feeding rates were reduced to 50% of that in controls (EC50) were also calculated.

Population dynamics in Daphnia magna as modified by chronic tetradifon stress.

Two Daphnia magna offsprings (animals from the first and third brood) whose parentals (F0-generation) were exposed during 21 days to different tetradifon (4-chlorophenyl 2,4,5-trichlophenyl sulfone) concentrations, were transferred to a pesticide free medium during 21 days (recovery period). The algae Nannochloris oculata (5 x 10(5) cells/mL) was used as food. In this recovery study, survival, growth and reproduction (mean total young per female, mean brood size, onset of reproduction and mean number broods per female) were assessed as individual parameters and the intrinsic rate of natural increase (r) as population parameter, for F1 generation (1st and 3rd broods). Reproduction was still reduced in F1 (1st and 3rd broods) generation daphnids from parentals (F0) exposed to 0.18 mg/L tetradifon and higher concentrations even after 21 days in clean water. However, survival was not significantly different (p > 0.05) in those F1 offsprings from parentals pre-exposed to the acaricide. Growth was still reduced in F1 daphnids from parentals pre-exposed to 0.10-0.44 mg/L tetradifon. The intrinsic rate of natural increase (r) was still affected in F1 generation daphnids, specially in those from the third brood. Therefore, F1 generation D. magna offsprings from a parental generation (F0) previously exposed to the acaricide tetradifon were not able to recuperate completely when a recovery period of 21 days was allowed.

Daphnia magna feeding behavior after exposure to tetradifon and recovery from intoxication.

The feeding behavior of the cladocera Daphnia magna subjected to a short-term exposure to the acaricide tetradifon (4-chlorophenyl 2,4, 5-trichlorophenyl sulfone) was studied. The experiments were performed using the unicellular algae Nannochloris oculata at a density of 5x10(5) cells/ml as food for the organisms. In a first experiment, three generations (F0, F1, and F3) of the daphnids were exposed to sublethal levels of tetradifon (0.1, 0.18, 0.22, and 0.44 mg/l) and the effect of the toxicant on filtration and ingestion rates was determined. Rates of filtration and ingestion of D. magna declined in the three generations studied with increasing toxicant concentrations; however, toxicant effect was greater in daphnids from generations F1 and F3 than in those from the parental generation F0. A second experiment was conducted in order to evaluate whether animals of a first (1) or third (F3) generation coming from parental daphnids (F0) previously exposed to those pesticide concentrations exhibited any alteration in feeding behavior when transferred to clean water (recovery period). The results indicated that the feeding rates of D. magna generations F1 and F3 were still affected during the recovery period but to a less degree. The effective tetradifon concentrations D. magna at which feeding rates were reduced to 50% that of controls (EC(50)) were also calculated.