Comparison of whole effluent toxicity with substance based hazard of produced water discharged by Norwegian platforms

Abstract

At the beginning of the millennium OSPAR policy on produced water discharges focused on oil in water and the application of Best Available Technique (BAT) and Best Environmental Practice (BEP) associated with oil. In 2009 the OSPAR Offshore Industry Committee (OIC) agreed to set up an Intersessional Correspondence Group on development of a risk-based approach (RBA) for the management of produced water discharges (ICG-RBA), with the task of developing a proposal for a holistic approach for the management of produced water discharges from offshore installations. This was referred to as the risk based approach. The ICG-RBA also developed the draft OSPAR Recommendation 2012/5 for a risk-based approach to the management of produced water discharges from offshore installations and associated Guidelines, that were adopted by OIC in 2012. OSPAR provided guidelines which allow both Whole Effluent Toxicity (WET) testing and a Substance Based (SB) approach (using the substance composition), or a combination of these approaches to be used to assess the risk of produced water (PW) discharged. The goal is to continuously reduce the overall risk to the environment. There is an ongoing debate on the comparability and complementarity of these two approaches. In the OSPAR SB approach, risk is calculated using PNECs mainly based on chronic toxicity data and are therefore based on lower assessment factors compared to the OSPAR WET based approach, where only acute toxicity data is generated and a maximum assessment factor (1000) is used. Furthermore, no attenuation factors (biodegradation, evaporation etc.) are accounted for in dilution/dispersion modelling in the WET approach, while this is accounted for in the formal SB approach. The present study focused on comparing hazards rather than risks of the two approaches to minimize dissimilarities between the methods e.g. by using similar toxicity data on similar test species and not account for fate processes such as biodegradation. The purpose of doing this was to determine how well both approaches agree with each other and whether the substances identified and selected included in the SB approach sufficiently cover the hazard of the produced water, indicating how well substances with toxicity (and risk) contribution are accounted for in Environmental Impact Factor (EIF) calculation of PW discharges on the Norwegian Continental Shelf (NCS). The present study evaluated the hazard of 25 PW effluents sampled at 25 platforms of 6 different operators on the NCS that WET tests were undertaken for (step 3, Phase 2 of the Norwegian implementation plan; Annex 4). Both a WET based and a SB approach was used to estimate the acute hazards (rather than risk) by attempting to use similar input data at same conditions (e.g., exposure duration, test species and toxicity endpoints), such that these approaches could be compared in the best possible way, with as little noise as possible. How well EIF substances cover the risk of a produced water discharge could not be concluded directly from the present...

Critical review of the OSPAR risk‐based approach for offshore‐produced water discharges

“…In a similar study by M. Reed et al (1996), organic acids and aliphatic hydrocarbons were found to be the main drivers of PW ecotoxicity. In a study by de Vries and Jak (2018) covering PW from 25 platforms in the North Sea, aliphatic hydrocarbons, organic acids, and PCs were found to be the biggest contributors, while the contributions of phenols and PAHs were negligible. A similar study of 12 platforms in the Bass Strait found sulfide, aromatic hydrocarbons, and ammonia to be the main ecotoxicity drivers and cyanide, metals, and phenols to be negligible (Parkerton et al, 2018).…”

“…This suggests that the multiphase characteristics of PW make it difficult to conduct the standard ecotoxicity tests on the mixture, especially long‐term tests. This is also highlighted by the difficulty of meeting validity criteria of standard ecotoxicity testing when testing PW, as reported by de Vries and Jak (2018). In their standardized ecotoxicity tests of PW from 25 platforms, 20 tests met the validity criteria defined in the ISO test for Vibrio fischeri , but only 11 and 10 met those of Acartia tonsa and Skeletonema constatum tests, respectively.…”

“…In their standardized ecotoxicity tests of PW from 25 platforms, 20 tests met the validity criteria defined in the ISO test for Vibrio fischeri , but only 11 and 10 met those of Acartia tonsa and Skeletonema constatum tests, respectively. Only PW from six platforms fulfilled the validity criteria of all three tests (de Vries & Jak, 2018). This is important, since compliance with validity criteria of standardized ecotoxicity test methods is a cornerstone in determining the regulatory reliability of ecotoxicity test results, and only results that are assessed as “regulatory reliable” can be used to derive the PNEC required in the RBA (ECHA, 2008).…”

“…The quantification of risk expressed as the PAF and msPAF allows for a comparison of the WET and SB approach. A study by de Vries and Jak (2018) compared the outcomes of using the WET and SB approach in the RBA on PW samples from 25 platforms within the OSPAR region. The WET approach predicted a higher risk more often than the SB approach, thus representing a more conservative approach (albeit only slightly), while the SB approach provided valuable information about the drivers of ecotoxicity.…”

Comparison of Substance‐Based and Whole‐Effluent Toxicity of Produced Water Discharges from Norwegian Offshore Oil and Gas Installations

“…When the latter database did not contain information on a required substance (group) the inter‐species correlation estimate was used. Because data on PAHs are scarce and variable (De Vries & Jak, 2018), EC50 data from the databases above were supplemented with information from Verbruggen (2012).…”