Review of Dredging Elutriate Application Factors: Relevance to Acute-to-Chronic Protection, Contaminant, and Endpoint Specificity.

摘要

The purpose of this technical report is to review the use of application factors (AFs) in determining the limiting permissible concentration (LPC) for water column (elutriate) toxicity evaluations for dredged material placement operations. Application factors are used as multipliers; AFs are applied to median effect toxicity endpoints in an effort to determine safe contaminant levels in the open water environment. While the default AF in the Marine Protection Research and Sanctuaries Act is 0.01, Federal regulations allow use of justifiable alternatives. An underprotective, high AF would underestimate the toxic effects of contaminants and potentially impact the organisms at the open-water, dredged material placement site. However, an overly conservative, low (excessively restrictive) AF would needlessly impose volume restrictions and increase dredged material management needs and costs. Herein the authors identify cases where use of the default AF is too conservative or even inappropriate: examples include situations in which it is applied to short-exposure-duration dredging placement operations (e.g., < 24 hours) where the exposure concentrations are decreasing steadily over time; instances in which it is applied to non-persistent contaminants and to inappropriate toxicological endpoints. Particularly, use of the default AF is overly conservative when high levels of non-persistent chemicals such as ammonia are present in elutriate water, and when toxicity is assessed using the very sensitive embryo/larval development tests. Since the default AF was not originally intended to be applied to nonpersistent contaminants or larval development endpoints, the authors propose alternatives to the default AF that is specific to ammonia toxicity and the development toxicity test endpoint.