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Biomedical subjects

G C Mitchell

Publications and source records attributed to G C Mitchell.

8 recordsLinked to original sources
PubMed2000

Development of methods to assess the effects of xenobiotics in outdoor artificial streams.

Two collaborative research projects were designed to develop and validate methods for determining the chronic effects of xenobiotics in freshwater ecosystems. The work reported here focuses on the development of methods for measuring effects on fish, invertebrates, and algae in outdoor artificial streams. 3,4-Dichloroaniline (3,4-DCA), has been used as a reference xenobiotic in two artificial stream experiments. The first used five stream channels: a control and treatments ranging from 70 to 2400 microg/liter. The second used eight stream channels--a control and treatments ranging from 0.45 to 4700 microg/liter and four coupled, 510-liter-capacity, downstream ponds-a control and treatments of 1.7, 37, and 820 microg/liter. Effects on the biota of the stream channels and the downstream ponds were examined using a range of sampling techniques and in situ toxicity tests.

Aniline Compounds↗
PubMed2000

Development of methods for evaluating toxicity to freshwater ecosystems.

This article presents a summary of a collaborative research program involving five European research groups, that was partly funded by the European Commission under its Environmental Research Program. The objective of the program was to develop aquatic toxicity tests that could be used to obtain data for inclusion at Level 2 of the Risk Evaluation Scheme for the Notification of Substances as required by the 7th Amendment to EC Directive 79/831/EEC. Currently only a very limited number of test methods have been described that can be used for this purpose and these are based on an even smaller number of test species. Tests based upon algae (Chlamydomonas reinhardi, Scenedesmus subspicatus, and Euglena gracilis), protozoa (Tetrahymena pyriformis), rotifera (Brachionus calyciflorus), crustacea (Gammarus pulex), and diptera (Chironomus riparius) were developed. The tests encompassed a range of end points and were evaluated against four reference chemicals: lindane, 3, 4-dichloroaniline (DCA), atrazine, and copper. The capacity of the tests to identify concentrations that are chronically toxic in the field was addressed by comparing the effects threshold concentrations determined in the laboratory tests with those determined for similar and/or related species and end points in stream and pond mesocosm studies. The lowest no-observed-effect concentrations (NOEC), EC(x), or LC(x) values obtained for lindane, atrazine, and copper were comparable with the lowest values obtained in the mesocosms. The lowest chronic NOEC determined for DCA using the laboratory tests was approximately 200 times higher than the lowest NOEC in the mesocosms.

Aniline Compounds↗
PubMed2000

Derivation of predicted No-effect concentrations for lindane, 3, 4-dichloroaniline, atrazine, and copper.

Environmental risk assessment is a key feature of regulations controlling the placing of new, and the maintenance of existing, chemicals products in the market place. For example, European Commission Directive 93/67/EC on Risk Assessment for New Notified Substances and Commission Regulation (EC) No. 1488/94 on Risk Assessment for Existing Substances requires that risk assessments be carried out for new and existing substances in the European Community. The process of environmental risk assessment seeks to determine the balance of probability of species and communities being damaged by chemical releases. The process relies upon a valid estimation of a predicted environmental concentration (PEC) in relevant environmental compartments and a predicted no effect concentration (PNEC) below which the organisms present in that compartment are unlikely to be significantly affected. If the PEC exceeds the PNEC there is a potential for damaging effects to occur. This article focuses on the determination of PNECs for risk assessment. Methods for determining a PNEC described in OECD Monograph 26 (1989, Report of the OECD Workshop on Ecological Effect Assessment, Paris, France, have been applied to data derived for the four chemicals lindane, 3,4-dichloroaniline, atrazine, and copper in a series of collaborative research projects funded by the European Commission.

Aniline Compounds↗
PubMed1993

Effects of lindane on macroinvertebrates and periphyton in outdoor artificial streams.

A system of six outdoor artificial streams (dimensions 5.0 X 0.35 X 0.25 m) was used to study the biological effects of lindane in flowing water. Lindane was continuously applied during 28 days to four of the streams while two were left as untreated controls. The nominal concentrations were 4.0, 8.0, 16.0, and 32.0 micrograms liter-1 and the mean measured concentrations of lindane in stream water over 28 days were 3.1, 5.7, 11.1, and 20.3 micrograms liter-1. Effects were observed on population densities of the freshwater shrimp Gammarus pulex, drift of G. pulex and mayflies (Baetis spp.), and on community photosynthesis. An increase in photosynthetic production of oxygen, a result of increased periphyton standing crop, followed the loss of macroinvertebrates, via drift, from the treated streams. This established a clear link between a direct effect of lindane on macroinvertebrates and an indirect effect on periphyton production. Drift and community photosynthesis were the most sensitive of the biological parameters measured and effects were detected in all treated streams. During a 28-day experiment with lower concentrations of lindane, nominally 0.25 and 1.0 micrograms liter-1, there were minor effects on the drift of Baetis spp. but only at the higher concentration. There were no detected effects on population densities or on community photosynthesis. Results from the two experiments provided a measured no observed effect concentration for lindane of 0.2 micrograms liter-1 and the threshold concentration for sustained effects on the stream communities was in the range 0.8 to 3.1 micrograms liter-1.

Animals↗
PubMed1991

An outdoor artificial stream system designed for ecotoxicological studies.

Six outdoor artificial streams were designed to simulate natural stream environments. Their primary intended use is to define acceptable threshold toxicity concentrations for chemicals and effluents in the aquatic environment and so provide data that can be used to define water quality criteria more accurately than is possible on the basis of data obtained solely from laboratory tests. Each stream was divided into pool and riffle sections that were colonized by communities of periphyton and invertebrates. They were operated as partly flow-through, partly recirculating systems. The design and construction of the streams are described in detail, and brief descriptions are given of methods of establishing aquatic communities, measuring water quality parameters, and treating the streams with chemicals and effluents. The performance of the streams in environmental research is illustrated by reference to typical data for primary production, for invertebrate diversity and abundance, and for chemical concentrations measured during an experiment of two weeks duration.

Animals↗
PubMed1972

Vampire bat control by systemic treatment of livestock with an anticoagulant.

The blood of beef cattle given single doses (1 milligram per kilogram of body weight) of diphenadione (2-diphenylacetyl-1,3-indandione) became toxic to vampire bats (Desmodus rotundus) and remained toxic for 3 days without harming the cattle. Cattle at three ranches in Mexico treated with single intraruminal injections of diphenadione experienced a reduction in vampire bat bites of 93 percent. Bioassays of milk and liver from cattle treated orally with diphenadione in the laboratory indicated that there were no residue problems.

Administration, Oral↗