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C J van Leeuwen

Publications and source records attributed to C J van Leeuwen.

9 recordsLinked to original sources
PubMed2003

Evaluation of EU risk assessments existing chemicals (EC Regulation 793/93).

An evaluation was performed on the first group (41) of completed risk assessments for chemicals of the EU priority lists (Existing Chemicals; EC Regulation 793/93). The evaluation focussed on the conclusions of the risk assessments. The EU risk assessment process detected a high number of substances of concern. Furthermore priority chemicals may pose potential risks to the whole range of protection goals of the risk assessment. The predictability of the risk assessments for priority chemicals was investigated. Our a priori knowledge on possible risks of priority chemicals is found to be poor, especially for consumers. Both for environment and human health the potential risks were linked with a broad spectrum of use patterns. It is concluded that no industry category can in advance be excluded from performing risk assessments. For a great number of chemicals, additional testing was found to be needed to finalize the risk assessment. This evokes questions about the completeness of the current base-set, but also about the suitability of some of the submitted human health tests that should initially fulfil the base-set needs. The results of this evaluation are useful for ongoing discussions on risk assessment processes for chemicals.

European Union↗
PubMed2000

Classifying environmental pollutants: Part 3. External validation of the classification system.

In order to validate a classification system for the prediction of the toxic effect concentrations of organic environmental pollutants to fish, all available fish acute toxicity data were retrieved from the ECETOC database, a database of quality-evaluated aquatic toxicity measurements created and maintained by the European Centre for the Ecotoxicology and Toxicology of Chemicals. The individual chemicals for which these data were available were classified according to the rulebase under consideration and predictions of effect concentrations or ranges of possible effect concentrations were generated. These predictions were compared to the actual toxicity data retrieved from the database. The results of this comparison show that generally, the classification system provides adequate predictions of either the aquatic toxicity (class 1) or the possible range of toxicity (other classes) of organic compounds. A slight underestimation of effect concentrations occurs for some highly water soluble, reactive chemicals with low log K(ow) values. On the other end of the scale, some compounds that are classified as belonging to a relatively toxic class appear to belong to the so-called baseline toxicity compounds. For some of these, additional classification rules are proposed. Furthermore, some groups of compounds cannot be classified, although they should be amenable to predictions. For these compounds additional research as to class membership and associated prediction rules is proposed.

Animals↗
PubMed1994

Uniform system for the evaluation of substances. I. Principles and structure.

In April 1994, the first version of the Uniform System for the Evaluation of Substances (USES 1.0) was launched to comply with an action point of the Netherlands National Environmental Policy Plan. USES is a tool for the rapid, quantitative assessment of the hazards and risks of chemical substances, including new substances, existing substances, agricultural pesticides and biocides. It was developed to be applied as a decision-support system by the central government, by industry and institutes in the private sector and by international fora. Since hazard and risk assessment must be transparent to all users and easy to perform, USES 1.0 is well documented and available as a computer program. An overview of this system will be presented including its objectives, the national and international framework, the general principles involved, as well as the structure and the content of the models used.

Animals↗
PubMed1994

Application of QSARs in risk management of existing chemicals.

QSAR-estimates of aquatic toxicity of relatively unreactive (narcosis-type) organic chemicals for 19 species were used to predict "no-effect-levels" (NELs) at the ecosystem level by means of several extrapolation models which were recently discussed by the Organisation for Economic Cooperation and Development (OECD). It appeared that the differences between the numerical results of these extrapolation methods, despite their different statistical assumptions, were small. Equilibrium-partitioning theory for sediment and water as well as biota and water was used to derive NELs for aquatic sediments and whole-body residues. Simple equations are given, from which NELs for water, and subsequently for sediments and whole-body residues, can be predicted on the basis of only the octanol-water partition coefficient. Actual application of the models presented absolutely requires the availability of methods to recognize chemicals that act by the unspecific mechanism of narcosis. To this end, a classification scheme, based on molecular structure, was developed. This classification scheme was applied to the approximately 2000 so-called High Production Volume Chemicals (HPVCs) listed in Annex 1 of the Council Regulation on the Evaluation and the Control of the Environmental Risks of Existing Chemicals of the European Communities. From the classification of these 2000 HPVCs it is concluded that, for a large portion of all existing chemicals, reliable QSAR estimates of aquatic toxicity can be made; this considerably speeds up the process of priority setting and risk assessment of existing chemicals. The validity of this (dual) approach was tested by a comparison of estimated NELs with actual FCC values for all compounds from the US-EPA Water Quality Guidelines list that classify as narcosis-type compounds. This comparison shows that for many existing chemicals QSARs may be used to derive quality guidelines for water, aquatic sediments and residues in aquatic biota.

Amphibians↗
PubMed1994

Improvements in creatinine methodology: a critical assessment.

A large evaluation study, analytical as well as clinical, was performed on four published improvements for the determination of creatinine in serum. Two of the methods were based on the Jaffé reaction, the other two were enzymatic methods. Analytically, all four methods showed a similar performance. In the analysis of numerous specimens from advanced care departments, however, the methods performed differently. The two enzymatic procedures scored better than the two Jaffé methods, when compared with an HPLC-based reference method. However, even the best methods produced outliers and a larger scatter than that obtained with "normal" specimens.

Bilirubin↗
PubMed1987

Effects of chemical stress on the population dynamics of Daphnia magna: a comparison of two test procedures.

Ten substances were tested to compare two methods that can be used in chronic toxicity studies with the Cladoceran Daphnia magna. In semistatic experiments with cohorts (life-table studies) survival appeared to be a dominant factor in exponential population growth. Specific inhibition of reproduction as a result of toxic stress was observed only in tests with bromide and 2,4-dichloroaniline. For some substances (cadmium, bichromate, metavanadate, and bromide) individual growth (carapace length) was found to be a sensitive parameter. In intermittent-flow experiments with small expanding populations the yield (carrying capacity) proved to be a highly sensitive parameter, probably owing to the fact that in these tests populations grow logistically, i.e., become additionally stressed by food limitation. Chemically induced reductions in food ingestion and conversion efficiency may thus become very predominant. In view of the place of these crustaceans in the food web such reductions in the carrying capacity would seem to be of great ecotoxicological importance.

Aniline Compounds↗
PubMed1985

The use of cohorts and populations in chronic toxicity studies with Daphnia magna: a cadmium example.

Two semistatic life table experiments with Daphnia magna were carried out on reconstituted and Lake IJssel water. The "nontoxic concentrations" for cadmium with respect to the intrinsic rate of natural increase, derived from age-specific survival and fecundity were 1 and 3.2 micrograms/liter, respectively. Body length appeared to be a sensitive parameter. A third intermittent-flow experiment was started with small, exponentially growing populations. These populations had a stable age distribution, were composed of cohorts of different ages and showed an almost perfect logistic growth. Cadmium was shown to reduce the upper numerical limit (carrying capacity) for D. magna and was inversely related to this parameter: log Y = 2.85 -0.20 log [Cd]; r = -0.99. A "nontoxic concentration" could not be established. Based on the "background" concentration of cadmium, a freshwater quality criterion of 0.1 microgram/liter is proposed. The results are used to discuss several shortcomings of the current methods. Finally it is stated that the introduction of the concepts of population dynamics in reproduction tests with D. magna is a realistic step towards ecotoxicology.

Actuarial Analysis↗