No abstract

The present study describes the development of a 42-d chronic sublethal sediment toxicity test using the estuarine amphipod Melita plumulosa (Zeilder). This test was shown to predict the toxicity of metal-contaminated sediments previously found to adversely affect benthic community structure. Metals initially were tested individually by spiking reference sediment under conditions that ensured low metal concentrations in pore waters. Fertility was the most sensitive sublethal endpoint for copper- and zinc-spiked sediments, whereas cadmium-spiked sediments were not toxic to M. plumulosa, despite their high bioaccumulation of cadmium. The 42-d chronic sediment test was reproducible; however, variation between reference sediments collected from the same field location over time or from different locations did affect the reproduction of M. plumulosa. Sensitivity of M. plumulosa to metal-spiked sediments suggested that the interim sediment-quality guidelines (ISQGs) were too conservative. However, toxicity testing of sediments collected from field sites known to affect community assemblages significantly (p < 0.001) reduced the fertility of M. plumulosa, reflecting benthic community survey results and supporting the ISQGs. Bioaccumulation of cadmium and copper by M. plumulosa was elevated following chronic exposure to both laboratory and field-contaminated sediments; however, zinc bioaccumulation could be measured only in M. plumulosa exposed to field-contaminated sediments.

In Australia, the collection of estuarine invertebrates from the field for whole-sediment toxicity tests is hindered because of temporal variability in their population densities and distributions. The present study aimed to develop culturing procedures for Melita plumulosa (Zeidler), an epibenthic and intertidal, deposit-feeding amphipod that is native to the southeastern coast of Australia. During a 28-d chronic exposure, the species was tested under a range of salinities (5-35 per thousand), temperatures (14-25 degrees C), and sediment particle sizes (sand to silt). Optimal culture conditions with respect to salinity, temperature, sediment particle size, feeding, and light regimes were determined. Compared to survival, amphipod growth and fertility were better predictors of optimal culture conditions. A life-history experiment was undertaken at the initial culture conditions of 22 degrees C and 35 per thousand salinity to establish the age at maturity, length of reproductive cycle, and life span for each sex. Under these test conditions, posthatch female M. plumulosa released their first offspring at seven weeks, after which each female produced an average of nine juveniles every 16 d. Male M. plumulosa had an average life span of eight months, whereas females had an average life span of 11 months. Optimal culturing conditions established in the present study have been incorporated into toxicity test procedures with this species and are being used to maximize reproductive output of this species in laboratory cultures to provide a supply of juveniles for routine use in whole-sediment toxicity tests.

The sensitivities of juvenile and adult amphipods to metals (Cd, Cu, Ni, Pb, and Zn) in whole sediment and water-only exposures were compared using a newly developed acute test with the estuarine species Melita plumulosa. Endpoints included survival and bioaccumulation in adults, and survival and growth (body length) in juveniles over 96 h water-only and 10 day sediment exposures. Juveniles were more sensitive than adults to metals, either bound to sediments or in the aqueous phase. Although LOEC values for copper and zinc in juvenile whole-sediment tests (820 and 2290 mg/kg dry weight, respectively) were high in comparison with interim sediment quality guideline values for individual metals (270 and 410 for copper and zinc respectively), they were generally within the range of concentrations found in contaminated sediments in local estuaries. Accumulation of metals, together with the low porewater metal concentrations in whole-sediment tests, indicated that the ingestion of sediment is an important source of zinc and copper and cause of toxicity in this species.

No abstract