Meta-analysis of intrinsic rates of increase and carrying capacity of populations affected by toxic and other stressors.

Most of the thousands of substances and species that are of concern for environmental management will not be investigated empirically at ecologically relevant levels because of financial, practical, and ethical constraints. To allow risk assessment for these less well-known categories, we have developed a mechanistic model with classical equations from toxicology and ecology. The parameters are linked to well-known properties, such as the octanol-water partition ratio K(ow), acute lethal (body) concentrations, and organism size. This allows estimation of intrinsic rates of increase r and carrying capacity K over a wide range of substances and species. The model was calibrated with parameter values (micro +/- 95% confidence interval) obtained in reviews and validated by a meta-analysis with largely independent data from 200 laboratory experiments. For single substances, the 5 to 95% interval of the observations on intrinsic rates of increase overlapped with the range predicted by the model. Model and experiments independently indicated that population growth ceased below 1% of the acute median lethal concentration in about 5% of the cases. Exceptional values and possible explanations were identified. The reduction of the carrying capacity K was nearly proportional to the inhibition of the population growth r. Population-level effects of mixtures as estimated by concentration addition were confirmed by observations in the experiments. The impact of a toxicant and another stressor could generally be described by response multiplication, with the exception of cases with extreme stress. Data sets on population laboratory experiments are biased to metals and crustaceans. This field will benefit from empirical studies on chemicals, conditions, and species, identified as risky by the model. Other implications of the model for environmental management and research are discussed.

Responses in sediment bioassays used in the Netherlands: can observed toxicity be explained by routinely monitored priority pollutants?

In order to identify the cause of toxicity in sediments and suspended matter, a large number of samples with different degrees of contamination was taken at various locations in The Netherlands. Standard acute bioassays were carried out with the bacterium Vibrio fischeri, the rotifer Brachionus calyciflorus and the anostracan Thamnocephalus platyurus. Chronic standard tests were performed using the water flea Daphnia magna and larvae of the midge Chironomus riparius. Some novel bioassays were performed as well. Most toxic effects observed in standard bioassays with sediments from polluted sediments (class 3 and 4 on a scale of 0-4 according to the Dutch criteria) could be partly explained by toxic concentrations of known persistent priority pollutants, mainly heavy metals and occasionally polycyclic aromatic hydrocarbons. In some of the samples, ammonia toxicity was a confounding factor during testing. Suspended matter from the Meuse river at Eijsden, which may be considered as 'new' sediment (pollution class 2), was moderately to highly toxic in almost all bioassays. This could have been associated with a combination of heavy metals, PAHs and ammonia. At two locations from the Lake IJssel area with no apparent persistent pollution, moderate and strong effects were nonetheless observed in invertebrate tests. This might have been due to agricultural run-off of pesticides, which are not routinely measured in sediments. A few effects on V. fischeri in canals and a small stream could not be explained with standard chemical analysis, but seemed associated with the outlets of sewage water treatment plants and industrial effluents. Additional chemical analysis of pore water samples from five selected sediments yielded more identified substances such as phtalates, decanes, cosanes and fragrances, but it was estimated that their contribution to the effects observed on V. fischeri, D. magna and C. riparius was negligible.