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Monitoring surveys throughout America and Europe have demonstrated the widespread presence of organic synthetic substances such as pesticides and pharmaceuticals in surface water. To avoid deleterious effects on the aquatic system, many countries determine water quality criteria for pesticides. For each substance, the comparison of the concentration measured in water with its criterion gives an indication of the pressure this substance put on the aquatic system. However, in the environment, aquatic organisms are not only exposed to single pesticides but typically to mixtures of these substances. It is therefore of particular importance to take mixtures into account when defining water quality criteria, which is rarely done yet. We recently developed a method to define consistent and comparable water quality criteria for mixtures of herbicides having a similar mode of action. These criteria are calculated based on species sensitivity curves; the method assumes that these curves are parallel for substances having similar mode of action. The aim of this study was to apply our method to six organophosphates (insecticides) and to three β-blockers (pharmaceuticals), other groups of compounds commonly detected in surface water. We found some evidence that the developed methodology gives consistent results for these groups too. The hypothesis of parallelism was accepted in 2/3 (β-blockers) and 2/6 of the cases (organophosphates) for both species sensitivity curves based on effect concentrations 50% and on no-observed effect concentrations. The use of water quality criteria for mixture is illustrated by two case studies, which show the importance of taking mixtures into account in water quality legislation.

This study evaluated the usefulness of energy reserves as an early warning system in Folsomia candida when exposed to the pesticide dinoseb. After different exposure times, survival, reproduction, growth (weight and length), lipid and protein content of the organisms were determined. After six days of exposure at 15-30microg of dinoseb/g dry soil, the weight, lipid, and protein content of the exposed organisms were higher than the controls. This stimulation seems to indicate that Collembola adopt a strategy of increasing their growth in order to improve their reproduction. This hypothesis was confirmed by the number of eggs laid which was greater in exposed organisms. After 21 days, all measured parameters decreased. The results show that after having produced an effort to increase growth and reproduction, lethality increases. The selected energy reserves are not more sensitive than the classically measured parameters such as reproduction, but can be more predictive for a pollutant stress encountered by the organisms.

Multigeneration tests are very useful for the assessment of long term toxicity of pollutants such as endocrine disruptor compounds. In this study, multigeneration reproduction tests adapted from the ISO standard 11267 were conducted with the Collembola Folsomia candida. Springtails were exposed to artificial soil contaminated with four insect growth regulators (methoprene, fenoxycarb, teflubenzuron, and precocene II) according to two different experimental set-ups. In the first set-up, the parental generation (F(0)) of Collembola was exposed to a pollutant for 28 days. Juveniles from the F(1) generation were transferred to uncontaminated soil for another 28-day period to generate the F(2) generation. In the second set-up, the F(0) generation was exposed to a pollutant for 10 days before being transferred to uncontaminated soil to reproduce. After 18-28 days, juveniles from the F(1) were transferred to clean soil to generate the F(2) generation. An effect on the number of hatched juveniles of the F(2) generation was observed for methoprene after exposure of the F(0) for 28 days and hatching of F(1) in contaminated soil. For methoprene and teflubenzuron, significant effects were even observed on the F(2) generation with the second experimental set-up, when only the F(0) generation was exposed for 10 days. This shows that the impact of these substances is transgenerational, which can have important consequences for the population of these or other organisms. No effect on the F(2) generation was observed with fenoxycarb and precocene II with the 10-day exposure experiment. Our results show that the developed experimental procedures are appropriate to assess the long term effects of endocrine disrupting compounds on the reproduction of the non-target species F. candida. Another important finding is that two substances with the same predicted mode of action (i.e., the two juvenile hormone analogues fenoxycarb and methoprene) do not necessarily affect the same endpoints in F. candida.

Models describing dose-response relationships are becoming increasingly popular in ecotoxicology. They allow simple and thorough evaluations of toxicity test results, including inter- and extrapolations to concentrations or exposure times other than those tested. Simple parametric regression models are of particular interest because their parameters may be attributed mechanistic meanings and they can be applied without sophisticated mathematical and computational support. We recently proposed a four-parameter logistic regression model to fit the survival data of Daphnia magna under dinoseb stress. The model parameters are the maximum survival time, the minimum time required for an individual to die, effect concentration, EC(50), and a curve shape parameter. This model has now been applied to compare the lethality and reproduction toxicity of D. magna and the growth inhibition of Pseudokirchneriella subcapitata under dinoseb stress. It can be fitted adequately to all the measured data and the parameters can be attributed biological meanings in any of the three endpoints. A comparison of the modeled concentration-response functions of all three endpoints for dinoseb toxicity shows that the range of ECs with respect to both D. magna and algae is steep (a decrease of between 0.1 and 0.6 mg/L). The survival and reproduction of D. magna exhibit similar characteristic concentration-response functions and toxicities. The statistical no-effect concentration (SNEC) is 0.14 (survival) and 0.11 (reproduction)mg/L, respectively. On the other hand, algae seem to be less sensitive to dinoseb than D. magna (SNEC: 0.48 mg/L). However, further investigations of individual algae may lead to a more suitable comparison. We speculate that the four parameters of the model function can be related to specific properties of chemicals and organisms. Characterization of these properties would allow simple and appropriate estimation of the toxic effects of these chemicals.