Study of treated and untreated oil based drilling waste using a biomarker approach: gill and liver histopathology in Atlantic salmon (Salmo salar).

Abstract

In order to safely dispose and use treated drill cuttings waste oil based mud, it is important to obtain knowledge about the contamination levels for possible adverse effects in freshwater organisms. Selected biomarkers were studied in Atlantic salmon (Salmo salar) exposed to treated and untreated drill cuttings waste (OBMs). The fish were exposed for 14 days in a continuous flow system to nominal concentrations of 0.1 and 1 ppm drill cuttings waste. Sampling was done 3 times during the exposure period but only samples at 14 days of exposure were object of histopathological analysis. Polycyclic aromatic hydrocarbons and heavy metal content in the freshwater were analysed at the end of the exposure period. Histopathological biomarkers of effect were studied then in gills and liver of fish by means of image analysis. Results showed that gills and liver were severely damaged with the high untreated group (1 ppm) to a lower extent with the high treated group and no considerable effects with the control. Dunnett’s test was performed (only for gills data) to test and highlight the significant difference between exposed groups in comparison to the control. The affected gills were mostly damaged by aneuryisms, epithelial lifting and necrosis probably due to constituents of the mineral oils or heavy metals. The lack of proofs of the liver data made statistical analysis impossible for the liver histopathology. Particularly noteworthy is the sensitive response of this high order biomarker of effect compared to those at lower organisation level in this study, and compared to similar responses in another study where salmon exposed to crude oil.