Application of Neutral Red Retention Assay in the clam Ruditapes philippinarum and the crab Carcinus maenas as a screening tool for sediment quality assessment in marine environment

Dredged material can cause several negative impacts to the ecosystems. Its management is a key issue for the protection of the aquatic environments. Sediment quality guidelines alone are not able to estimate the potential adverse effects that contaminants bound to sediment can cause. The in situ approach using caged bioindicator species has been chosen lately as a new sensitive tool for the assessment of dredged material. In a tier testing approach, Neutral Red Retention Assay (NRRA) has been applied as a screening tool in order to detect adverse changes in health status associated to contaminated environments. Nevertheless, to the authors' knowledge, little is known about the application and validation of NRRA in sediment bioindicator species and under field conditions. Caged Ruditapes philippinarum and Carcinus maenas were exposed during 28 days to 3 potentially contaminated sites in the Algeciras Bay (SW Spain) and to a reference site in the Cadiz Bay (SW Spain). Health status of exposed organisms was measured through NRRA in haemolymph samples. No significant differences of Neutral Red Retention Time (NRRT) were measured neither in clams nor in crabs over time in the organisms from control site (70 ± 10min). However significant differences (p < 0.05) were found at the end of the exposure period in clams and crabs exposed to contaminated sediments from Algeciras Bay, showing a decrease of NRRTs from 30 to 70% compared to the control organisms. The results obtained confirmed the use of NRRA as a suitable and sensitive method to be used in the assessment of sediment quality.