Chemical contamination and the ecological quality of surface water
Baas, J. and Kooijman, S. A. L. M.
Chemical contamination and the ecological quality of surface water.
Envir. Pollut. 158: 1603 - 1607
To assess the quality of surface waters, the typical procedure that is
followed that a land use survey is conducted and based on this the
concentration of contaminants in the surface water is monitored. The
concentration of all the measured contaminants is subsequently
compared with their respective Maximum Permissible Concentrations
(MPCs). This approach leads to a number of questions, most importantly
(assuming that the right contaminants measured): How bad is it if MPCs
are exceeded? And: Is the water quality good if no MPC are exceeded?
We tried to answer these questions by comparing MPCs to observed and
calculated effects of contaminants in Dutch surface waters. We show
that there are shortcomings underlying the concepts of the MPCs. And
therefore we can not be sure that the water quality is okay if MPCs
are not exceeded. Neither can we be certain that the water quality is
not safe (for 95 % of all species) if MPCs are exceeded. The lack of
relation between exceeding MPCs and mortality amongst in situ exposed
daphnids underlines this. It is possible to have a daphnid population
go extinct within 30 hours of exposure when it is exposed to a mixture
of metals or pesticides at the concentration level of the maximum
permissible concentration. We conclude that the MPCs aim to protect
95% of all species is not met for a number of compounds taken up in
our analysis. Especially if organisms are exposed to mixtures of
metals or pesticides, as they are in the environment, the objectives
of the MPCs are not met. Specifically the MPC for cadmium and the ad
hoc MPC of 2 ng/l that is used for some pesticides are not strict
enough. Especially for the more potent insecticides, like diazinone.