The use of a biomarker to assess the effect of xenobiotic exposure on the freshwater invertebrate Gammarus pulex.

Contamination of freshwaters is of concern because of its effect on ecosystem
health. The effect of contamination can be assessed at all levels of biological
organisation, from the ecosystem level to the molecular level. At the biochemical
level, enzymes that are involved in the detoxification of organic chemical
contaminants are useful as markers of contaminant exposure as they are often one
of the first systems to respond to chemical exposure. Furthermore, changes in the
activity of these enzymes may be indicative of effects at higher levels of biological
organisation. In this study, the use of the detoxification enzyme glutathione stransferase
(E. C. 2.5.1.18) (GST) in the freshwater invertebrate Gammarus pulex
(Crustacea: Amphipoda), as a biomarker of organic xenobiotic exposure and
effects was assessed. Toxicant induced changes in GST activity were related to
changes in energy status and physiological energetics.
A GST assay was developed that allowed the rapid analysis of GST activity in up
to ninety individual animal samples simultaneously. Optimum sample handling
and assay conditions were determined for the assay of GST in G. pulex, and
extrinsic factors (e. g. environmental temperature, feeding and holding conditions)
and intrinsic factors (e. g. body size), affecting variability of GST activity in
G. pulex were assessed The effect of exposure to the organic xenobiotics
lindane( an organochlorinein insecticide) and alcohol ethoxylate( a non-ionic
surfactand detergent)on GST activity in G.pulex was described. The magnitude
and duration of the response of GST activity to exposure to both chemicals was
assessed under laboratory conditions and with alcohol ethoxylateu, sing outdoor
artificial streams.
The use of GST as a marker of pesticide exposure in field populations of G. pulex
that were subject to pesticide contamination was studied in comparison with
animals from non-contaminated, reference sites. The differences in GST activity
between animals from a contaminated site and clean site were investigated by
short-term and long-term exposure to lindane in the laboratory. Changes in
energy status and physiological energetics were investigated in G. pulex on
exposure to lindane by measuring glycogen concentration and scope for growth.
Measuring these parameters on short-term and long-term exposure to lindane
allowed the sensitivity of these responses to be related to the GST response and
allowed the energetic cost of exposure to be assessed.
It was concluded that increase in GST activity may providea rapid and sensitive
biomarker of xenobiotic exposure in the short-term and in populations subject to
pesticide contamination. The affect on GST activity may be indicative of effects
at higher levels of biological organisations, such as scope for growth and glycogen
concentration However, GST activity is affected by a variety of intrinsic and
extrinsic factors and should therefore be used only asp art of a comparative study.
Because of the transient nature of the GST response in situ assessments should
be based on 24-hour exposure periods.