Ecotoxicology

A rather small data matrix of seven chemicals and 17 different ecotoxicological end points is examined by methods of Discrete Mathematics. Especially, the lattice theory and its variant, the Formal Concept Analysis may be an attractive tool to analyze Quantitative Structure Activity Relationships, when a numerical functional approach is not at hand. The central item is the so called concept, which is a pair of subsets: A subset of molecules and a subset of properties which correspond to each other. The concepts are partially ordered due to a subset relation. From this subset relation, if–then-rules are derived, which aim to relate the structure of molecules with their ecotoxicological properties. For example, the following chemical rule is found: Cl ⇒ (2A,2C,2M). That means, all substances considered here having a “–Cl” as structural code have a medium ecotoxicological effect on Daphnia magna , Orconectes immunisare (Crustacea) and on Photobacterium phosphoreum , at least within the training set.

Terrestrial risk assessments for pesticide exposure is generally based on a limited number of toxicity data. The protection target for these assessments requires an extrapolation from species for which toxicity data are available to other species with unknown sensitivity to be able to protect these as well. Our ability to extrapolate toxicity endpoints between species is a major source of uncertainty in risk assessment. Most analyses of interspecies extrapolation in avian risk assessments have dealt with acute toxicity data. It was suggested that, in the absence of a strong rationale to the contrary, we should assume that reproductive data is at least as variable as acute data and that strategies developed for acute data could be applied to long term toxicity data as well. Considering only the two main bird test species for which reproduction data are available (Mallard and Northern Bobwhite), a comparison of the interspecies standard deviation for both acute and reproduction data suggests that the two are equally variable. Analysis of a very limited data set also suggests that this conclusion holds regardless of which endpoint is triggered in the reproduction study. However, the relative sensitivity of the two species established from acute test data appears to be reversed in the case of reproductive data. In addition there seems to be no reason to believe that bodyweight is a factor in helping birds cope with the rigours of chronic dosing, which is in contrast with the acute dosing situation. This suggests that the best extrapolation technique for reproduction test data should be independent of phylogeny and independent of bodyweight scaling. The simplest such method is the one that was proposed by Luttik and Aldenberg (1995, 1997) for both birds and mammals.

We examined the effects of sublethal doses of an organophosphorus insecticide, Methyl Parathion (MeP), on the foraging behaviour of honeybees (Apis mellifera ligustica) in a flight cage. The results revealed that MeP modified the frequency of visits to a feeding station to which the bees had previously been trained. A dose of 50 ng per animal elicited an increase in the frequency of visits to the feeder, compared to control animals. A dose of 10 ng, on the other hand, led initially to a decrease in the visit frequency, followed by an increase to a level above that of the controls. A hypothesis is presented to account for the way in which MeP affects foraging behaviour. We propose that the behavioural assay presented here could be useful as a preliminary screening test to study sublethal effects of pesticides on foraging performance in honeybees.

We measured a suite of common biomarker responses for the first time in the Sydney rock oyster Saccostrea glomerata to evaluate their utility as biological effects measures for pollution monitoring. To examine the relationship between biomarker responses and population level effects, fertilisation and embryo development assays were also conducted. Adult oysters were deployed in two contaminated estuaries and a reference estuary in Sydney, Australia. The concentrations of various contaminants (metals and polycyclic aromatic hydrocarbon, PAHs) were quantified in oyster’s tissue from each site and both metals and total PAHs were significantly elevated in contaminated estuaries relative to the reference estuary. Lysosomal membrane destabilisation, lipid peroxidation levels and glutathione (GSH) concentrations were measured in the digestive gland of oysters. Of all biomarkers measured, lysosomal membrane destabilisation proved to be the most useful indicator of oysters facing anthropogenic stress and we suggest this may be an especially useful biomarker for incorporation into local environmental monitoring programs. Moreover, lysosomal membrane destabilisation showed good correlations with fertilisation, normal embryo development and estuary status. GSH and lipid peroxidation were not as valuable for distinguishing between estuaries exposed to differing levels of anthropogenic stress, but did provide additional valuable information regarding overall health status of the oysters.

Despite a wealth of information on biomarkers, they are not routinely used for regulatory purposes, even though the potential benefits of biomarkers to rationalise complex exposure–response relationships are clear. Biomarkers can be inappropriately applied or misinterpreted, because the fundamental assumptions in exposure–response relations have not been considered. Factors causing temporal and spatial variability in biomarker responses are reviewed. These include numerous geochemical and biotic variables. The variation can be minimised by appropriate study site selection, experimental replication, multivariate epidemiological approaches, normalised controls, and temporal calibration of responses; so that the regulatory use of biomarkers for biomonitoring and tracking pollution events, including chronic or multiple exposures to complex mixtures is possible. We propose and define the characteristics of biomarkers of chronic exposure or effect, which must measure changes in pollution/effect against long-term changes in other general stresses (disease, nutrition, environmental quality), relate to cumulative injury, and remain responsive over months or years. Neuroendocrine, immunological, and histological biomarkers are suggested for chronic pollution. We propose a regulatory framework for biomarkers based on a weight of evidence approach that can integrate biomarkers in risk assessment and long-term monitoring programmes.

Higher-tier ecological risk assessment (ERA) in mesocosms is commonly performed in lotic or lentic experimental systems. These systems differ in their physico-chemical and hydrological properties, leading to differences in chemical fate, community characteristics and potential recovery. This raises the issue of the relevance and sensitivity of community-level endpoints in different types of mesocosms. In this study, macroinvertebrate abundance and biomass estimates were used to assess the effects of a dithiocarbamate fungicide, thiram (35 and 170 µg l−1), and a petroleum middle distillate (PMD; 0.01, 0.4, 2 and 20 mg l−1) in outdoor stream and pond mesocosms. Streams were continuously treated during 3 weeks followed by a 2-month long post-treatment period. Ponds were treated weekly for 4 weeks, followed by a 10-month long post-treatment period. Taxonomic structure of macroinvertebrate communities was characterized using the α, β and γ components of taxa richness, Shannon and Gini-Simpson indices. Computations were based either on abundance or biomass data. Results clearly highlighted that the effects of chemicals depended on the exposure regime (for thiram) and type of system (for the PMD). Causes of the differences between streams and ponds in the magnitude and nature of effects include differential sensitivity of taxa dwelling in lentic and lotic systems and the influence of hydrology (e.g., drift from upstream) and mesocosm connectivity on recovery dynamics. This study also showed complementarities in the use of both types of mesocosms to improve the characterization of chemical effects on communities in ERA.

The main focus of environmental endocrine disruption is understanding how hormone mimics may be affecting reproduction and development. The principle mode of action for hormones is to regulate gene expression. The vitellogenin mRNA assay described in this paper was developed to study the specific mechanisms of action by proposed xenoestrogens. The establishment of this method is widely applicable to different species and to different genes. This gene specificity is what makes it such a good method to characterize a particular mechanism of action. Vitellogenin was chosen due to its current value as a plasma protein biomarker for estrogen exposure. The vitellogenin mRNA assay serves as a valuable complement to plasma vitellogenin, as it increases the sensitivity of detection as well as its potential to detect an earlier estrogenic response. Once validated, it can be used in biomonitoring as an effective method to detect a specific mechanism of action in samples exposed to xenoestrogens.

Crustaceans are major constituents to aquatic ecosystems that provide a variety of ecological and economic services. Individual crustacean species are adept at occupying diverse niches and their success, in part, stems from neuro-endocrine signaling cascades that regulate physiology in response to environmental and internal cues. Peptide hormones are major signal transducers in crustaceans. The crustacean hyperglycemic hormone family of peptides regulates various aspects of growth, reproduction, and metabolism. These peptides may function as the terminal hormone to regulate some physiological activities or may function as intermediates in a signaling cascade. Ecdysteroids and terpenoids are two major classes of terminal signaling molecules in these cascades. Hormones from these two classes function independently or in concert to regulate various processes. Ecdysteroid signaling is subject to toxicological disruption through disturbances in ecdysteroid synthesis or binding of toxicants to the ecdysteroid receptor. Methyl farnesoate is the major terpenoid hormone of crustaceans and also is susceptible to disruption by environmental chemicals. However, the methyl farnesoate signaling pathway is poorly understood and only limited mechanistic confirmation for disruption of this endocrine signaling pathway exists. Disruption of the ecdysteroid/terpenoid signaling pathways in crustaceans has been associated with aberrations in growth, metamorphosis, reproductive maturation, sex determination, and sex differentiation. Population studies have revealed disruptions in crustacean growth, molting, sexual development, and recruitment that are indicative of environmental endocrine disruption. However, environmental factors other that pollution (i.e., temperature, parasitism) also can elicit these effects and definitive causal relationships between endocrine disruption in field populations of crustaceans and chemical pollution is generally lacking.