Critical evaluation of an intercalibration exercise undertaken in the framework of the MED POL biomonitoring program

The results of an intercalibration exercise among the laboratories particip ating in the MED POL program for monitoring biological effects of pollutant s along the Mediterranean coasts are presented. Three established biomarker s, i.e. lysosomal membrane stability, metallothionein concentration and eth oxyresorufin-O-deethylase (EROD) activity, were intercalibrated. The stabil ity of lysosomal membranes in mussels (Mytilus galloprovincialis Lam.) was assessed with a cytochemical method. The four participating laboratories we re able to discriminate between control animals (membrane labilization time s ranging from 21 to 35 min) and Cu-exposed animals (40 mu g/l Cu for 3 day s) (labilization times ranging from 4.5 to 7.4 min). The metallothionein co ncentration was evaluated in digestive gland homogenates of control mussels and of animals exposed to 200 mu g/l Cd for 7 days. The eight participatin g laboratories were able to discriminate between controls and treated sampl es using a spectrophotometric method. The EROD activity was evaluated by 11 laboratories. All laboratories were able to discriminate between liver mic rosomal preparations obtained from control and from benzo-a-pyrene exposed fisk(Dicentrarchus labrax), with values ranging from 0.5 to 15.88 pmol/min/ mg protein in controls and from 5.41 to 165.13 pmol/min/mg protein in treat ed animals. Using S9 fractions, it was possible to correctly identify contr ol and treated fish, with a variation similar to that found using microsoma l fractions, albeit with an inevitable difference in specific activity. As a corollary, all laboratories involved produced comparable data and were ab le to identify pollutant-induced stress syndromes in sentinel organisms. Th us, intercalibration enables the use of biomarkers in large biomonitoring p rograms. (C) 2000 Elsevier Science Ltd. All rights reserved.