Multi-tool assessment of trace metals in mangroves combining sediment and clam sampling, DGT passive samplers and caged mussels.

The rapid loss of mangroves globally has triggered a call for a better understanding of this habitat, including its dynamics and the threats it is exposed to. The present paper reports the study of trace metals at nine mangrove sites in Singapore in 2012/2013, using the simultaneous application of various tools, namely sediment analyses, the technique of diffusive gradients in thin-films (DGT) and caged/native bivalves (for both chemical and biomarker analyses). DGT devices were successfully deployed over 28days in tropical mangrove waters, and the concentration measured with DGT showed significant correlation with the accumulation for Cu, Zn and Cd in caged mussels, and Cu for native clams, supporting the relevance of DGT to predict metal bioaccumulation. Concentrations in mangrove sediment are reported for As, Cd, Co, Cr, Cu, Ni, Pb and Zn. Sediment levels on a dry weight (dw) basis of Cu (ND-219.5μg/g dw) and Zn (ND-502μg/g dw) exceeded general sediment quality criteria at two sites. Most notably for these two metals, investigations based on the four tools (DGT, sediments, caged mussels and clams) were all able to segregate sites above and below the sediment quality guideline. This was further supported by a range of significant linear correlations between the measurements obtained with the various tools. The present findings support that these monitoring tools are comparable in the field to provide a time-integrated assessment of metals such as Cu and Zn.