Norway has since 1998 developed a policy based on the "Zero Harmful Discharge" principle regulating the discharges of produced water (PW) based on the potential environmental effects of its components. A challenge linked to this policy is to assess the risk for the marine environment associated to the main components in the discharges. This risk characterisation will ultimately determine the measure to be implemented on a platform such as chemical substitution, installation of additional PW cleaning technology. A second challenge is to document the environmental benefits of the selected technology in a "Zero harmful impact" perspective. This implies that environmental monitoring tools that can be applied in field and for which enough knowledge are available to conclude on the impact level. These challenges were addressed for the Ekofisk field where additional PW cleaning technology has been installed in order to meet the "Zero Harmful Discharge" objective. A joint industry project was launched to document the environmental benefit of the technology selected based on novel monitoring techniques. Blue mussel and cod were exposed to realistic concentrations of produced water from the Ekofisk field in controlled short and long term experiments to establish exposure and effect concentration threshold levels for a series of responsive biomarkers. These biomarkers were thereafter applied in field monitoring before and after implementation of improved PW treatment technology at the field. The monitoring confirmed a reduction of the environmental footprint measured by biomarkers together with a reduction in discharge of oil in PW. This environmental footprint is seen as individual effect in a limited area, smaller than the predicted risk area. The results confirm the value of bio-monitoring tools for assessing environmental impact linked to PW discharges, but also the conservatism built in the environmental risk management tool in use in Norway as a decision tool for selecting measures based on a cost-environmental benefit approach.

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