Nickel phase partitioning and toxicity in field-deployed sediments.

The pool of bioavailable metal in sediments can be much smaller than total metal concentration due to complexation and precipitation with ligands. Metal bioavailability and toxicity in sediment is often predicted from models of simultaneous extracted metal and acid volatile sulfide (SEM-AVS); however, studies of the applicability of these models for Ni-contaminated sediments have been conducted primarily in laboratory settings. We investigated the utility of the SEM-AVS models under field conditions: Five lotic sediments with a range of sulfide and organic carbon contents were amended with four concentrations of Ni, deployed in streams for eight weeks, and examined for colonizing macroinvertebrates. After four weeks, colonizing macroinvertebrates showed a strong negative response to the Ni-treated sediments and SEM-AVS models of bioavailability differentiated between toxic and nontoxic conditions. By Week 8, relationships deteriorated between colonizing macroinvertebrates and SEM-AVS model predictions. Total Ni in the sediment did not change through time; however, Ni partitioning shifted from being dominated by organic cabon at deployment to associations with Fe and Mn. Combined geochemical and toxicity results suggest that Fe and Mn oxides in surface sediments resulted in Ni being less available to biota. This implies that current SEM-AVS models may overestimate bioavailable Ni in sediments with oxic surface layers and sufficient Fe and Mn.

Effects of sublethal chronic copper exposure on the growth and reproductive success of the Florida apple snail (Pomacea paludosa).

Florida apple snails (Pomacea paludosa) were exposed to three concentrations of copper (Cu), in water (8 microg/L, 16 microg/L, 24 microg/L), for one generation to examine uptake and the effects on survival, growth, and reproduction of the F(0) generation and survival, growth, and whole body Cu of the F(1) generation. During a 9-month Cu exposure, apple snails exposed to 8-16 microg/L Cu had high Cu accumulation (whole body, foot, viscera, and shell) and significantly reduced clutch production (8-16 microg/L) and egg hatching (16 microg/L). Apple snails exposed to the 24 microg/L Cu had low survival and the treatment was therefore terminated. Concentrations of minerals (Na(+), K(+), Mg(2+), Ca(2+)) in tissues were maintained regardless of Cu exposure, but the distribution of Cu in the body of snails differed, depending on exposure concentrations. Higher exposure concentrations resulted in a greater percentage of Cu accumulated in the viscera of the snail. Copper exposure to the F(0) generation did not affect the survival, growth, or whole body Cu concentrations in the F(1) generation. These finding are significant, given the importance of the Florida apple snail in the Everglades food chain. Changes in the abundance of apple snail populations, as a result of Cu exposure, could ultimately affect foraging success of predators.

Copper desorption in flooded agricultural soils and toxicity to the Florida apple snail (Pomacea paludosa): implications in Everglades restoration.

Copper (Cu) desorption and toxicity to the Florida apple snail were investigated from soils obtained from agricultural sites acquired under the Comprehensive Everglades Restoration Plan. Copper concentrations in 11 flooded soils ranged from 5 to 234 mg/kg on day 0 and from 6.2 to 204 mg/kg on day 28 (steady-state). The steady-state Cu concentration in overlying water ranged from 9.1 to 308.2 microg/L. In a 28-d growth study, high mortality in snails occurred within 9 to 16 d in two of three soil treatments tested. Growth of apple snails over 28 d was affected by Cu in these two treatments. Tissue Cu concentrations by day 14 were 12-23-fold higher in snails exposed to the three soil treatments compared to controls. The endangered Florida snail kite and its main food source, the Florida apple snail, may be at risk from Cu exposure in these managed agricultural soil-water ecosystems.

Cross-species extrapolation of chronic nickel Biotic Ligand Models.

The use of Biotic Ligand Models (BLMs) to normalize metal ecotoxicity data and predict effects in non-BLM organisms should be supported by quantitative evidence. This study determined the ability of chronic nickel BLMs developed for the cladocera Daphnia magna and Ceriodaphnia dubia to predict chronic nickel toxicity to three invertebrates for which no specific BLMs were developed. Those invertebrates were the snail Lymnaea stagnalis, the insect Chironomus tentans, and the rotifer Brachionus calyciflorus. Similarly, we also determined the ability of chronic nickel BLMs developed for the alga Pseudokirchneriella subcapitata and the terrestrial vascular plant Hordeum vulgare to predict chronic nickel toxicity to the aquatic vascular plant Lemna minor. Chronic nickel toxicity to the three invertebrates and the aquatic plant were measured in five natural waters that varied in pH, Ca, Mg, and dissolved organic carbon (DOC), which are known to affect chronic nickel toxicity and are the important input variables for the chronic nickel BLMs. Nickel toxicity to the three invertebrates varied considerably among the test waters, i.e., a 14-fold variation of EC50s in L. stagnalis, a 3-fold variation in EC20s in C. tentans, and a 10-fold variation in EC20s in B. calyciflorus, but the cladoceran BLMs were able to predict nickel effect concentrations within a factor of two. Nickel toxicity (EC50s) to L. minor varied by 6-fold among the test waters. Although the P. subcapitata and H. vulgare BLMs offered reasonable predictions of nickel EC50s to L. minor, the D. magna and C. dubia BLM showed better predictions. Our results confirm the influence of site-specific pH, hardness, and DOC on chronic nickel toxicity to aquatic organisms, and support the use of chronic nickel BLMs to manage this influence through normalizations of ecotoxicity data.

Copper uptake and depuration by juvenile and adult Florida apple snails (Pomacea paludosa).

The present study characterized copper (Cu) uptake and depuration by juvenile and adult Florida apple snails (Pomacea paludosa) from water, soil, and diet. During a 28-day uptake period, juvenile apple snails were exposed to aqueous Cu and adult apple snails were exposed to Cu-contaminated soil, water, and food. In the follow-up 14-day depuration period, both juvenile and adult apple snails were held in laboratory freshwater with background Cu concentrations<4 microg/l. For juvenile apple snails, whole body Cu concentrations increased with time and reached a plateau after 14 days. The data followed Michaelis-Menten kinetics rather than a one compartment first order kinetics model. The mean Cu bioconcentration factor (BCF) for juvenile apple snails was 1493 and the depuration half-life was 10.5-13.8 days. For adult snails, dietary uptake of Cu resulted in higher bioaccumulation factors (BAFs) compared to uptake from soil. Most of the accumulated Cu was located in soft tissue (about 60% in the viscera and 40% in the foot). The shell contained <1% of the total accumulated copper. Soft tissue is usually consumed by predators of the apple snail. Therefore, the results of the present study show that Cu transfer through the food chain to the apple snail may lead to potential risk to its predators.