Ordination techniques for analysing response of biological communities to toxic stress in experimental ecosystems.

The ordination techniques principal component analysis (PCA) and redundancy analysis (RDA) are considered to be useful tools for evaluating community responses in experimental ecotoxicology. Concepts and interpretation of these techniques are summarized. Application of PCA and RDA is illustrated in a case study. In this study, the effects of a single application of the insecticide Dursban(®) 4E (a.i. chlorpyrifos) on an aquatic macroinvertebrate community in microcosms were analysed. Four treatment (nominal chlorpyrifos concentration: 35 µg l(-1)) and four control microcosms were used. PCA visualized a change in species composition with time. Immediately after treatment, a major shift in species composition occurred in treated microcosms. RDA demonstrated that this shift was due to the treatment. RDA also showed that non-arthropods were generally insusceptible to chlorpyrifos; most arthropods were affected. Dynamics of separate taxa were visualized, giving indications of possible primary and secondary effects for these taxa. A Monte Carlo permutation test was used to decide whether treatment had a significant effect on the species composition and to investigate the state of recovery in time. In general, the RDA results gave an adequate condensation of detailed information on abundance and effects obtained by more conventional univariate statistical analysis for some individual taxa of the community. In combination with toxicity and ecological data, ordination techniques can provide insight into effects of toxic substances in complex biological communities.

An evaluation of four types of freshwater model ecosystem for assessing the hazard of pesticides.

Experimental results are reported on four types of freshwater model ecosystem after administration of a single dose of chlorpyrifos. The fate, and primary and secondary effects of chlorpyrifos were compared between the model ecosystems, and were evaluated in the light of the predictive value of the current ecotoxicological hazard assessment procedure for pesticides. 'Slootbox', a fate model used in the ecotoxicological risk assessment of pesticides in the Netherlands, overestimated chlorpyrifos concentrations. The primary effects of chlorpyrifos can be predicted accurately on the basis of single species laboratory toxicity data. The population effects observed in the microecosystems, microcosms, and mesocosms were consistent between all experiments and with the single species tests. Community metabolism, as a functional endpoint, was less sensitive than the structural parameters measured. Secondary effects, both for structural and functional endpoints, varied between the micro- and mesocosm experiments. At the present 'state of the art' in ecotoxicology, no a priori prediction of secondary effects in natural ecosystems will generally be possible. 0.1 times the lowest acute L(E)C50 for chlorpyrifos, as measured in the current ecotoxicological hazard assessment procedure, matched the NOECmesocosm for a single dose of chlorpyrifos. Recovery of populations affected by insecticide stress was found to depend on factors such as life cycle characteristics and ecological infrastructure, in addition to the toxicant concentration. The onset of (potential) recovery is likely to start at an approximate concentration of the EC10(48 h).

Fate and effects of the insecticide Dursban 4E in indoor Elodea-dominated and macrophyte-free freshwater model ecosystems: I. Fate and primary effects of the active ingredient chlorpyrifos.

The fate of the insecticide Dursban 4E (active ingredient chlorpyrifos) and its effect on crustaceans and insects was studied in indoor experimental freshwater ecosystems that intended to mimick drainage ditches. A single dose (simulating aerial drift) was applied to achieve nominal chlorpyrifos concentrations of 5 or 35 micrograms/L. Two experiments were performed, one in which all model ecosystems were dominated by the macrophyte Elodea nuttallii, and one using systems devoid of macrophytes. In macrophyte-dominated systems, Elodea vegetation adsorbed a large proportion of the dose applied and hampered the mixing of the insecticide in the water (at least up till day 8). Only a small proportion became incorporated in the sediment. In open water systems the insecticide was rapidly mixed in the water, and the sediment played a very significant role as sink for chlorpyrifos. In both Elodea-dominated and open water systems 50% of the dose applied had disappeared on day 8 post-treatment. The rate of disappearance of chlorpyrifos was relatively rapid in water and macrophytes, and relatively slow in the sediment. Of the arthropods in the zooplankton Cladocera were more susceptible than Copepoda. Significant effects (p less than or equal to 0.05) on Cladocera occurred relatively late in Elodea-dominated systems (in week 4 post-application) in contrast to open water systems (week 1), which is in accordance with the observed differences in the fate of chlorpyrifos. Daphnia pulex, D. longispina and Simocephalus vetulus recovered in the model ecosystems when chlorpyrifos concentrations were lower than 0.1-0.2 micrograms/L, which is in agreement with results of laboratory protocol tests performed with these cladocerans. Among the macroscopic Arthropoda the apparent order of susceptibility was amphipods greater than insects greater than isopods. The isopod Asellus aquaticus was more sensitive to the application of the insecticide than the closely related species Proasellus coxalis. In treated open water systems the latter even increased significantly in numbers. Cage experiments in the model ecosystems performed with several species of Arthropoda indicate that laboratory protocol tests may give a reasonable prediction of short-term direct effects of chlorpyrifos for the same species inhabiting more complex aquatic systems.

Joint toxicity of mixtures of groups of organic aquatic pollutants to the guppy (Poecilia reticulata).

In this study acute lethal concentrations (LC50) to the guppy (Poecilia reticulata) were determined for mixtures of 4 groups of aquatic pollutants. The groups were composed of 11 nonreactive, nonionized organic chemicals, 11 chloroanilines, 11 chlorophenols, and 9 reactive organic halides. Earlier studies indicated that the joint toxicity within each of these groups was concentration additive, probably because of a similar mode of action. The joint toxicity of combinations of one representative from each group showed a high variance, but generally tended to be partially additive to concentration additive. This high variance is probably caused by the low number of compounds in these mixtures. Experiments with mixtures of whole groups gave more accurate results. The toxicity of a mixture of the first three groups, containing 33 well-known aquatic pollutants, was almost completely concentration additive. Concentrations of 0.04 of the individual LC50 values contributed to the toxicity of this mixture.

Quantitative structure-activity relationships and mixture toxicity of organic chemicals in Photobacterium phosphoreum: the Microtox test.

Quantitative structure-activity relationships were calculated for the inhibition of bioluminescence of Photobacterium phosphoreum by 22 nonreactive organic chemicals. The inhibition was measured using the Microtox test and correlated with the partition coefficient between n-octanol and water (Poct), molar refractivity (MR), and molar volume (MW/d). At log Poct less than 1 and greater than 3, deviations from linearity were observed. Introduction of MR and MW/d improved the quality of the relationships. The influences of MR or MW/d may be related with an interaction of the tested chemicals to the enzyme system which produces the light emission. The sensitivity of the Microtox test to the 22 tested compounds is comparable to a 14-day acute mortality test with guppies for chemicals with log Poct less than 4. The inhibition of bioluminescence by a mixture of the tested compounds was slightly less than was expected in case of concentration addition. The Microtox test can give a good estimate of the total aspecific "minimum toxicity" of polluted waters. When rather lipophilic compounds or pollutants with more specific modes of action are present, this test will underestimate the toxicity to other aquatic life.

Quantitative structure-activity relationships and mixture toxicity studies of chloro- and alkylanilines at an acute lethal toxicity level to the guppy (Poecilia reticulata).

Quantitative structure-activity relationships (QSARs) were calculated for the acute lethal toxicities (14-day LC50) to the guppy (Poecilia reticulata) of anilines, with several hydrophobicity characteristics and the Hammett sigma constant as parameters. Calculated and experimental Poct values and II constants were used as hydrophobicity characteristics. Introduction of Hammett constants improved the quality of the QSARs. Together with the QSAR studies the toxicities of mixtures of the anilines were determined. The toxicities of three mixtures did not deviate from concentration addition.

Hexachlorobutadiene residues in aquatic fauna from surface water fed by the river rhine.

Hexachlorobutadiene (HCBD) was identified as a component of the residue mixture of chlorinated hydrocarbons in fish from inland waters fed by the Rhine, particularly in the Ketelmeer. The residue level in fish is related to the fat content; no bioaccumulation in the food chain to higher trophic levels was observed. HCBD concentrations in the water of the Ketelmeer appeared to be three orders of magnitude lower than those found in aquatic animals.