| Summary: | The report presents results from the Water Column Monitoring 2009, performed in collaboration between NIVA and IRIS, with sub-contractors. The objective of the survey was to assess the extent to which produced water discharges from Ekofisk affect organisms living in the water column. The study was designed to monitor bio-accumulation and biomarker responses in organisms held in cages in the vicinity of the water discharge point(s). The study design was identical to that carried out at Ekofisk in 2006 and 2008 with only minor modifications where necessary. The implementation of a produced water treatment system (C-Tour), operational in 2008, aimed to reduce the output of potentially toxic chemicals into the surrounding water column. The monitoring surveys performed pre and post implementation of C-Tour, were designed to assess whether changes in animal health status between the different years have occurred. The results of the 2009 survey have shown that caged organisms were exposed to low levels of produced water components with highest tissue concentrations in mussels Mytilus edulis, located closest to the produced water discharge. Mussels located approximately 1-2 km away showed only background concentrations of the organic compounds measured. Concentrations of polycyclic aromatic hydrocarbon (PAH) and alkyl phenol (AP)-metabolites in bile of caged cod Gadus morhua, were slightly elevated suggesting exposure at the Ekofisk stations. There was a signal of exposure with proximity to the discharge for some of the biomarkers measured including CYP1A in fish and micronuclei in mussels. However, all other fish and mussel biomarkers showed no significant exposure effects. The bioaccumulation data and biomarker responses indicated a lower exposure to the produced water effluent than seen previously in 2008 and 2006. The volume of produced water discharged to the investigated area increased in 2009 from 2008 and 2006. However, the amount of oil discharged with the produced water was less, resulting in an overall ...
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