Sequential non-destructive sampling of Atlantic cod (Gadus morhua) in a long term exposure to produced water chemicals

Abstract

A major concern related to production of oil from offshore installations is the discharge of produced water, which contains organic pollutants like PAHs (Polycyclic aromatic hydrocarbons) and APs (Alkylphenols) as well as metals and chemicals utilized in the production process. There are studies on the effect of produced water on benthic fauna, plankton and fish, but few on long term exposures under controlled conditions. The aim of this study was to investigate the long term effect of ecologically relevant dilutions of PAHs and APs found in produced water as well as how the effects change over time in individual fish. To achieve this, 90 cod (Gadus morhua) were exposed to these substances in three different exposure schemes for 44 weeks. Blood from each fish was sampled before starting the exposure and 7 set times throughout the study and analysed for several biomarkers. Amounts of Vitellogenin (VTG) and zona radiata protein (ZRP) were measured to investigate estrogenic effects; oxidative stress was assessed using the total oxyradical scavenging capacity (TOSC) assay; occurrence of micronuclei was used as an indicator for genotoxicity and hematocrit values and Fulton’s condition factor (CF) were used to evaluate effects on general health. In addition liver somatic index (LSI) and gonado-somatic index (GSI) was calculated for the last sample date. And the mortality of the fish was compared to fish only subject to one blood sample before starting the exposure. The statistical analyses showed no estrogenic effects, no effects on TOSC and no indication of genotoxicity in any of the treatments at any of the sample dates. The assessment of general health showed no differences in CF and LSI but some significant differences were detected in hematocrit values between treatments and the control group but these were not consistent throughout the experiment and they are concluded to be coincidental. An apparent correlation between the change in hematocrit values and condition factor was observed. Other studies have previously shown that exposure to produced water and as well as the chemicals we selected to have an effect on the same biomarkers that we used. However this study used a lower concentration than most other studies 5 The repeated blood sampling did appear to affect mortality after the 6th sample date. The mortality was 2.7 percentage points higher in the fish subject to repeated blood samples between the 6th and the 8th blood sampled taken (p=0.05), and 6.3 percentage points higher between the 8th and the 9th blood sampling (p=0.03) compared to fish only sampled once.