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three WLIS sediment samples was determined relative to a sediment sample collected from a 

 reference area in central Long Island Sound used for all ETC sediment laboratory control 

 toxicity tests. In addition, toxicity of the WLIS "A" and "D" samples was compared to 

 mortality rates observed with the WLIS 2000W sample. 



The test organism, Ampelisca abdita, was collected from surface sediments (upper 8 

 to 10 cm) of the Pettaquamscutt River, Narragansett, Rhode Island. Amphipods 0.71- 

 1.0 mm in size were held at the ETC in chambers containing presieved, uncontaminated 

 sediments from their original collection location under static water conditions. During 

 acclimation and holding, the amphipods were fed, ad libitum (as much as they could 

 consume), the laboratory cultured diatom Phaeodactylum tricornutum. Fifty percent of the 

 water in the holding containers was replaced every day at the time of feeding. 



Twenty-four hours prior to test initiation, each test sediment (WLIS "D," WLIS "A," 

 and 2000W) was press-sieved through a 2.0 mm mesh screen, homogenized, and placed into 

 exposure chambers. Five replicates were tested for each sediment. A fourth sediment 

 sample, collected from a reference area in central Long Island Sound, served as a laboratory 

 control sediment for the test. Each chamber received filtered seawater, was placed into 

 20° C water baths, and provided aeration. 



On test initiation day, August 15, aeration was stopped, and 20 subadult amphipods 

 were distributed randomly into each test chamber. After one hour, the containers were 

 checked for amphipods that had not burrowed into the sediment. The test was started when 

 nonburrowing animals were replaced and aeration restarted. The animals were not fed 

 during the test. 



Mortality was the endpoint for the Ampelisca toxicity test. The number of dead 

 amphipods in each chamber was recorded daily, and the dead organisms were removed. 

 Temperature was monitored daily during the test. Salinity, dissolved oxygen, and pH were 

 measured on Day 5 and Day 10 of the test. After ten days, the bioassay was terminated, and 

 the contents of each exposure container sieved through a 0.5 mm mesh screen. The material 

 retained on the sieve was sorted under a stereomicroscope and the recovered amphipods 

 counted. Any missing individuals were assumed to have died and decomposed during the 

 test and were counted as dead. 



Mortality data from the 10-day test established the toxicity of the WLIS sediments 

 relative to a laboratory control sediment and the toxicity of the WLIS "A" and "D" 

 sediments relative to the 2000W reference area sediment. Toxicity data were reported as 

 mean percent survival. A t-test (arc sine-square root transformation) determined statistical 

 differences on proportional mortality by comparing the test sediment data to the laboratory 

 control. 



Monitoring Cruise at the Western Long Island Sound Disposal Site, July 1992 



