Anatomy of a Decision: Part I―Potential Regulatory Outcomes from Changes in the Canadian Dredged Material Disposal at Sea Chemical Protocols

摘要

Background/Objectives. Environment Canada (EC) regulates the disposal at sea (DaS) ofdredged material (DM) in Canada using the legal authority of the Canadian EnvironmentalProtection Act, 1999 ([CEPA] 1999). Currently, the Tier 1 assessment involves the determinationof both the geophysical properties of the dredged material (sediment) and theconcentrations of four contaminants (Cd, Hg, PAH and PCB), as well as “other chemicals ofinterest” using analyte-specific lower action levels (LALs), specified in the regulations. Unlikedredged material disposal frameworks in many countries, CEPA does not apply chemicalupper action levels (UALs) within their framework. As part of an ongoing review, EnvironmentCanada’s DaS Program has hosted a workshop in 2006. A number of recommendationswere made concerning the development of sediment assessment tools, the interpretation ofthese tools, and the essential attributes of a comparative risk assessment process for dredgedmaterial management. Specific recommendations to improve chemical assessments includedreviews of the following issues: a) Inclusion of a broader suite of metals in Tier 1 assessments,b) Expansion of the PAHs examined in Tier 1 from the 16 parent compounds, c)Examination of PCBs based upon individual congeners rather than aroclors, d) Inclusion of abroader range of organic compounds in Tier 1 assessments, and e) Inclusion of chemicalUALs in the Tier 1 assessment. Since the workshop, EC has sought advice externally andcarried out work internally to address a range of issues in support of framework revisions;studies evaluated the scientific underpinnings of a number of assessment and decision tools,and reviewed international policy and practice on various aspects of the DM framework.Approach. It was strongly recommended that any changes to the framework should be precededby a field assessment that evaluated the potential responses of representative sedimentsfrom throughout Canada’s coastal and marine areas to a range of decision approaches. Such areview would evaluate whether an expanded, and potentially more expensive, assessmentapproach would change regulatory outcomes; whether it would “capture” potentially contaminatedsediments which were currently missed. However, field studies of sufficient size (andwith sufficient analyses) to test the impacts of various assessment and decision approachesare expensive, and currently outside the program’s budget. A more cost-effective approachwould be to challenge Tier 1 approaches using a “data mining” strategy. Such an approachcould identify sediment chemistry (and, ideally, co-located toxicity) datasets that are available,and subject them to a series of Tier 1 decision approaches to determine whether differentapproaches “classify” sediments differently in regulatory terms. Based on results, recommendationscould be made about a Tier 1 approach. To this end, a North American database wasbuilt with 2196 records of marine and estuarine sediment chemistry and, where available, colocatedbiology.