Methods for Identifying Causes of Toxicity in Whole-Sediments

Whole-sediment toxicity identification and evaluation (WS-TIE) is a relatively new approach for assessing the cause of toxic effects to benthic organisms in sediments. Akin to aqueous TIE methods, the premise of the WS-TIE method is that the chemical toxicant(s) responsible for observed effects can be identified through a series of treatments that are designed to reduce the bioavailability and, thus, toxicity of key contaminant classes. While standardised WS-TIE methods have been developed for a range of contaminants (US EPA, 2007), many contaminated sediments exist for which the methods can not adequately identify the cause(s) of toxicity. Standard WS-TIE methods primarily manipulate the toxicity of dissolved contaminants, but do not address effects that may occur via dietary exposure to chemical contaminants. The research presented herein, recognises that standard WS-TIE methods do not address all of the major contaminant exposure pathways for some benthic organisms. New WSTIE methods to address toxic effects of those contaminants acting via dietary exposure routes were developed as a part of this research. The new methods were specifically designed for whole-sediment toxicity tests using the epibenthic amphipod M. plumulosa; a deposit feeding species that can display acute toxicity from dietary exposure to contaminated sediments (Simpson and King, 2005; Mann and Hyne, 2008; Spadaro et al., 2008). WS-TIE methods using the microalgae Entomoneis cf punctulata were also developed to compliment results achieved using Melita plumulosa in sediment quality assessments. New WS-TIE treatments were developed to modify the organism’s exposure to sediment contaminants by modifying the bioaccessibility of particulate-associated contaminants (PACs) to M. plumulosa. The two new techniques were principally employed to achieve this goal. Firstly, a mesh exposure chamber (MEC) was developed that effectively prevented M. plumulosa from ingesting sediments, but did not modify the exposure to dissolved contaminants in the overlying water. Secondly, resins deployed at the sediment surface, metal chelating resin-top (MCR-Top) or carbonaceous adsorbent resin-top (CAR-Top) to both remove from the dissolved phase, metals and organic contaminants, respectively. It was demonstrated that sediment nutrition had a large influence on the outcome of whole-sediments toxicity tests, and a food addition (FOOD) treatment was incorporated into the suite of WS-TIE treatments to help differentiate between the natural effects caused by nutritionally-poor sediments and the toxic effects of dietary exposure to contaminants.