Effects of malathion and carbendazim on Amazonian freshwater organisms: comparison of tropical and temperate species sensitivity distributions

The risk assessment of pesticides for freshwater ecosystems in the Amazon has relied on the use of toxicity data and water quality criteria derived for temperate regions due to a lack of ecotoxicological studies performed with indigenous species. This leaves an unknown margin of uncertainty for the protection of Amazonian ecosystems, as differences in environmental conditions and species sensitivity are not taken into account. To address this issue, the acute toxic effects of malathion (an organophosphorus insecticide) and carbendazim (a benzimidazole fungicide) were assessed on five fish and five freshwater invertebrates endemic to the Amazonian region. Subsequently, the intrinsic sensitivity of Amazonian and temperate freshwater species was compared using the species sensitivity distribution (SSD) concept. Amazonian species sensitivity to malathion was found to be similar to that of their temperate counterparts, with LC50 values ranging between 111 and 1507 μg/l for fish species and 2.1–426 μg/l for arthropod species. However, Amazonian fish appeared to be slightly less sensitive for carbendazim than temperate fish with LC50 values ranging between 1648 and 4238 μg/l, and Amazonian invertebrates were found to be significantly more resistant than their temperate counterparts, with LC50 values higher than 16000 μg/l. The results of this study suggest that for these compounds, the use of water quality criteria derived with laboratory toxicity data for temperate species will result in a sufficient protection level for Amazonian freshwater organisms. Recommendations for further research include the validation of threshold concentrations derived with temperate standard test species and with the SSD model with semi-field experiments considering larger assemblages of indigenous species under local environmental conditions

Variability in the Dynamics of Mortality and Immobility Responses of Freshwater Arthropods Exposed to Chlorpyrifos

The species sensitivity distribution (SSD) concept is an important probabilistic tool for environmental risk assessment (ERA) and accounts for differences in species sensitivity to different chemicals. The SSD model assumes that the sensitivity of the species included is randomly distributed. If this assumption is violated, indicator values, such as the 50% hazardous concentration, can potentially change dramatically. Fundamental research, however, has discovered and described specific mechanisms and factors influencing toxicity and sensitivity for several model species and chemical combinations. Further knowledge on how these mechanisms and factors relate to toxicologic standard end points would be beneficial for ERA. For instance, little is known about how the processes of toxicity relate to the dynamics of standard toxicity end points and how these may vary across species. In this article, we discuss the relevance of immobilization and mortality as end points for effects of the organophosphate insecticide chlorpyrifos on 14 freshwater arthropods in the context of ERA. For this, we compared the differences in response dynamics during 96 h of exposure with the two end points across species using dose response models and SSDs. The investigated freshwater arthropods vary less in their immobility than in their mortality response. However, differences in observed immobility and mortality were surprisingly large for some species even after 96 h of exposure. As expected immobility was consistently the more sensitive end point and less variable across the tested species and may therefore be considered as the relevant end point for population of SSDs and ERA, although an immobile animal may still potentially recover. This is even more relevant because an immobile animal is unlikely to survive for long periods under field conditions. This and other such considerations relevant to the decision-making process for a particular end point are discussed

Sensitivity of macroinvertebrates to carbendazim under semi-field conditions in Thailand: Implications for the use of temperate toxicity data in a tropical risk assessment of fungicides

The present paper discusses the fate of the fungicide carbendazim (nominal concentrations: 0, 3.3, 33, 100 and 1000 mu g L(-1)) and its effects on the macroinvertebrate community in outdoor microcosms set up in Thailand. Fate and threshold values were subsequently compared with those noted in temperate model ecosystem studies in order to evaluate to which extent toxicity data generated in temperate regions for compounds like carbendazim may be extrapolated to tropical areas. Carbendazim disappeared faster from the water column than reported in temperate model ecosystem studies, which is explained by a possibly greater microbial breakdown of the fungicide under the tropical conditions tested. The No Observed Effect Concentration (NOEC) calculated in the present study for the macroinvertebrate community was the same as recorded in a study carried out in The Netherlands (3.3 mu g L(-1)). However, most sensitive representatives in the latter study were "worm-like" taxa, whereas water boatmen (Corixidae) were the most sensitive macroinvertebrates in the present study. The ecological realism of a tropical risk assessment based on temperate organisms that are less sensitive than local macroinvertebrates may be questionable. Recommendations for future research include testing the possibility to rear sensitive representatives of indigenous Thai Corixidae in the laboratory and conducting model ecosystem studies evaluating a wider range of pesticides on a larger tropical geographical scale. (c) 2008 Elsevier Ltd. All rights reserved

Effects of the antibiotic enrofloxacin on the ecology of tropical eutrophic freshwater microcosms

The main objective of the present study was to assess the ecological impacts of the fluoroquinolone antibiotic enrofloxacin on the structure and functioning of tropical freshwater ecosystems. Enrofloxacin was applied at a concentration of 1, 10, 100 and 1000µg/L for 7 consecutive days in 600-L outdoor microcosms in Thailand. The ecosystem-level effects of enrofloxacin were monitored on five structural (macroinvertebrates, zooplankton, phytoplankton, periphyton and bacteria) and two functional (organic matter decomposition and nitrogen cycling) endpoint groups for 4 weeks after the last antibiotic application. Enrofloxacin was found to dissipate relatively fast from the water column (half-dissipation time: 11.7h), and about 11% of the applied dose was transformed into its main by-product ciprofloxacin after 24h. Consistent treatment-related effects on the invertebrate and primary producer communities and on organic matter decomposition could not be demonstrated. Enrofloxacin significantly affected the structure of leaf-associated bacterial communities at the highest treatment level, and reduced the abundance of ammonia-oxidizing bacteria and ammonia-oxidizing archaea in the sediments, with calculated NOECs of 10 an

Environmental and human risks of pesticide use in Thailand and Sri Lanka; results of a preliminary risk assessment

Currently, a major difficulty facing the establishment of sustainable management plans in complex agricultural systems in the tropics is the lack of sufficient relevant information on important ecological, hydrological and land use processes that underpin the various values generated by natural resources. By applying baseline information from two study sites in Thailand and Sri Lanka, the MAMAS project aims at developing cost-effective tests and other environmental diagnostic tools that can ultimately be used in an integrated risk assessment model, leading to the development of policy guidelines for the management of agrochemical use in aquatic systems in Asian countries. The initial stage of the project involved a situation analysis which was followed by a preliminary risk assessment as described in this report. The preliminary risk assessment was aimed at gathering further information on the environmental characteristics of the study sites, in order to estimate potential risks (to both human health and the environment) through pesticide exposures. The information gathered within the MAMAS project was used to model the exposure concentration of the pesticides towards aquatic communities and residues present in food items. This exposure assessmentwas compared with estimated safe concentrations for the environment and human health. Both the environmental and the human health assessment indicated large potential risks. These risks were not only present for the farm channels located next to the cropbut also for larger aquatic systems such as cascade tanks present in Sri Lanka. The next phase of the project will consist of performing chemical measurements, bioassays and biomonitoring (the Triad approach). Data obtained will be used to validate the procedures used in the preliminary risk assessment

Use, fate and ecological risks of antibiotics applied in tilapia cage farming in Thailand

The use, environmental fate and ecological risks of antibiotics applied in tilapia cage farming were investigated in the Tha Chin and Mun rivers in Thailand. Information on antibiotic use was collected through interviewing 29 farmers, and the concentrations of the most commonly used antibiotics, oxytetracycline (OTC) and enrofloxacin (ENR), were monitored in river water and sediment samples. Moreover, we assessed the toxicity of OTC and ENR on tropical freshwater invertebrates and performed a risk assessment for aquatic ecosystems. All interviewed tilapia farmers reported to routinely use antibiotics. Peak water concentrations for OTC and ENR were 49 and 1.6 µg/L, respectively. Antibiotics were most frequently detected in sediments with concentrations up to 6908 µg/kg d.w. for OTC, and 2339 µg/kg d.w. for ENR. The results of this study indicate insignificant short-term risks for primary producers and invertebrates, but suggest that the studied aquaculture farms constitute an important source of antibiotic pollution

Fate and effects of the insecticide chlorpyrifos in outdoor plankton-dominated microcosms in Thailand

The fate and effects of the insecticide chlorpyrifos were studied in plankton-dominated, freshwater microcosms in Thailand. Disappearance rates of chlorpyrifos from the water column in the present study were similar to those in temperate regions. Insecticide accumulation in the sediment was relatively small, with the major part in the top layer (depth, 1.5 cm). Application of chlorpyrifos led to significant changes in freshwater biological communities. Clam shrimps (Conchostraca) and the cladoceran Moina micrura were the most susceptible species (no-observed-effect concentration [NOEC], 0.1 mu g/L) and macroinvertebrates the most sensitive community (NOEC, 0.1 mu g/L). These results are in agreement with those from semifield experiments with chlorpyrifos in temperate regions. The results of an in situ bioassay were used to calculate a NOEC of 0.1 mu g/L and a 48-h median lethal concentration of 0.6 mu g/L for M. micrura, which are similar to toxicity values reported for Daphnia magna in studies in temperate regions. Overall, these findings support the use of toxicity data from temperate regions for the risk assessment of low-persistent insecticides like chlorpyrifos for aquatic communities in tropical regions