Brain acetylcholinesterase activity as biomarker in a polluted river: comparative responses in two fish species

FERNANDO R. DE LA TORRE; FERRARI, L.

Liege Belgica

Congreso; XXI Congress European Society for Comparative Physiology and Biochemistry; 2000

European Society for Comparative Physiology and Biochemistry

The Reconquista river is a heavily polluted water course of Buenos Aires (Argentina) receptor of industrial and domestic pollutants characterised by an important pollution gradient from upstream towards its mouth.  Fish have been extensively used as toxicity test organisms. Cnesterodon decemmaculatus (Poecilidae) is an indigenous freshwater micro-omnivorous fish present in the waterbodies of Buenos Aires Province present in the river, Cyprinus carpio on the other hand is an exotic species widely distributed, being used as sentinel organism in toxicity bioassays.  The aim of the study was to evaluate the toxic effect of a polluted watercourse by means the biomarker responses of brain AchE assessed under field cage conditions for C. carpio, and in situ collection for C decemmaculatus. Adult females of C. decemmaculatus were sampled upstream (Cascallares) and in a middle site (San Francisco) located 5 and 21 km from the mouth of the river during summer and autumn (CnCas and CnSF1,CnSF2 and CnSF3 respectively). Control fish were taken from a non-polluted pond located in the University campus near the river.  Two bioassays were conducted on summer with juvenile C carpio (CyCas1) and (CyCas2); fish were maintained in polypropylene cages for 30 days at Cascallares. Surface water samples were taken at each sampling moment in order to determine their physicochemical profile.  Acetylcholinesterase activity (AchE) was evaluated according to the method of Ellman et al.  Statistical differences were calculated with Student t test (p<0.05).  The eserine 50% inhibitory concentration (IC50) (used as an AchE specific inhibitory referent ) was calculated for both species using the Inhibition concentration (Icp) Approach recommended by USEPA. The measured physicochemical parameters in many cases were higher than those established by the local legislation for the protection of freshwater life even in Cascallares.  Brain AchE activities were inhibited in all fish groups collected in SF (19-31% respect to control groups). In Cas, AchE fish showed a variable trend: CnCas fish did not differ from controls, but AchE activities were inhibited in CyCas3 but not in CyCas2.  AchE results were compared with the inhibitory potency of eserine in in vitro assays.  Data showed that C decemmaculatus is much more resistant to eserine. Chemical analyses of the river water samples have shown that they were devoid of organochlorine and organophosphorous insecticides. However, AchE values suggested that fish had been exposed to punctual insecticides discharges which can only be detected by a continnuous monitoring of the river water. The evaluation of this specific biomarker has shown to be a useful tool to check the insecticide exposure in natural water bodies.