Pore water is considered a primary route of contaminant exposure to benthic organisms. Used with solid-phase sediment evaluations, toxicity of pore water provides additional insight into the bioavailability of contaminants to benthic organisms. However, toxicity and chemistry of pore water change in response to sediment disturbance, and the complex chemistry commands careful interpretation of results. The objective of this study was to evaluate the influence of a one-week equilibration period (sediment storage) on pore-water toxicity. To accomplish this, toxicity of pore water collected immediately after stirring the sediment was compared with that of pore water collected after one week of equilibration (sediment stored in the dark at 4oC). Toxicity was determined using percent survival of Hyalella azteca exposed (static) for 96 hours to pore water collected from the sediment with vacuum extractors. Toxicities of contaminated sediments were generally more pronounced in pore waters collected after one week of equilibration compared to those extracted immediately after stirring. Alkalinity, hardness, conductivity and ammonia increased and pH decreased following sediment storage. Although increases in toxicity of some pore waters were attributed to the elevated ammonia concentrations, toxicities of some pore waters were due to other factors such as contaminants. Pore-water assessment is a useful tool in the determination of sediment quality, but standard operating procedures that include specific guidance on sediment disturbance and storage time (equilibration period) after disturbance should be followed to reduce variability and enhance interpretation of test results.

Introduction

Pore water is a primary route of contaminant exposure to benthic organisms. Used with solid-phase testing, pore water provides additional insight into sediment bioavailability of contaminants. However, toxicity and chemistry of pore water change in response to sediment disturbance and storage time, and the complex chemistry of pore water commands careful interpretation of test results. Disturbance (stirring) of the sediment during solid-phase testing increases the turbidity and amount of material in the pore water, thus influencing the availability of contaminants in the pore water. Storage or holding of disturbed sediment should allow an equilibrium between the sediment and pore water to re-establish itself. This study was undertaken in order to evaluate the influence of sediment storage time/equilibration on pore-water chemistry and toxicity.

Objective

Determine the influence of sediment equilibration (sediment storage after disturbance) on the toxicity and chemistry of pore water.

Methods and Materials

Results and Discussion

Equilibration (storage) of sediments tended to increase the toxicity of pore water. Pore waters that were toxic initially generally became more toxic, and several (14% of this data set) that were not toxic in the initial tests became toxic after sediment storage for eight days. Of the 23% (20 samples) that decreased in toxicity, only 8% (2 samples) were significantly less toxic. Only 14% (12) of the samples showed no difference in survival (toxicity). Some increases in toxicity were attributed to increases in ammonia and alkalinity that occurred during storage; however, some metals increased in the pore water also. Hardness and conductivity also increased in the pore water with storage, but pH decreased.

Summary and Conclusions