Fate of isotopically labeled zinc oxide nanoparticles in sediment and effects on two endobenthic species, the clam Scrobicularia plana and the ragworm Hediste diversicolor

Although it is reported that metal and metal oxide nanoparticles, which are among the most rapidly commercialized materials, can cause toxicity to organisms, their fate in the environment and toxicity to marine organisms are not well understood. In this study, we used a stable isotope labelling approach to trace the fate of nanoparticles (NPs) in sediments and also investigated bio-uptake in two estuarine intra-sedimentary invertebrates Scrobicularia plana and Nereis diversicolor. We selected exposure to 3 mg kg(-1) sediment ZnO NPs since this level is a realistic prediction of the environmental concentration in sediments. (ZnO)-Zn-67 NPs (DLS: 21-34 nm, positively charged: 31.3 mV) suspensions were synthesised in diethylene glycol (DEG). We explored the fate of (ZnO)-Zn-67 NPs in sediment, Zn-67 bioaccumulation and the biochemical (biomarkers of defence and damage) and behavioural (burrowing kinetics and feeding rates) biomarkers in both species to (ZnO)-Zn-67 NPs and DEG on its own during a 16 d laboratory exposure. After exposure, Zn-67 concentrations in sediment showed higher levels in the upper section (1 cm: 2.59 mg kg(-1)) decreasing progressively (2 cm: 1.63 mg kg(-1), 3 cm: 0.90 mg kg(-1), 4 cm: 0.67 mg kg(-1)) to a minimum value at the bottom (5 cm: 0.31 mg kg(-1)). Zn-67 bioaccumulation was observed in both organisms exposed to (ZnO)-Zn-67 NPs in DEC but no major inter-species differences were found. At the biochemical level, (ZnO)-Zn-67 NPs exposure significantly induced increased glutathione-S-transferase activity in worms and catalase activity in clams whereas superoxide dismutase activity and thiobarbituric acid reactive substance levels were not affected in any species. Exposure to DEC on its own leads to a significant increase of metallothionein-like protein levels in clams compared with those exposed to (ZnO)-Zn-67 NPs or controls. Burrowing behaviour as well as feeding rate were significantly impaired in both species exposed to (ZnO)-Zn-67 NPs. Concerning exposure to DEC on its own, burrowing behaviour impairments were also shown in both species and feeding rate was impaired in bivalves. At environmentally realistic concentration of (ZnO)-Zn-67 NPs in sediment, there is no strong evidence for a severe nanoparticle effect since most effects were also observed in the presence of DEC alone. (C) 2012 Elsevier Inc. All rights reserved.