Soil elemental analysis in a high conservation tropical forest in Singapore.

To understand the distribution of soil elemental concentrations and their potential sources of trace metal contamination in the high-conservation Nee Soon freshwater swamp forest in Singapore, we analyzed samples from 227 surface and 35 subsurface (auger profiles) locations. Our assessment involved distribution maps, principle component analysis, cluster analysis, and correlation analysis of element concentrations determined from a mixed acid digestion and measurement on an ICP-MS. We found a distinct zonation in the distribution of several elements (Ba, Cr, Cu, Fe, Mn, Pb, Sr, Ti, V, and Zn) between the upper and lower catchment that gives an erroneous notion of widespread contamination in the lower catchment. We believe this zonation is natural, likely related to differences in the underlying geology. However, Cu, Pb, and Sb concentrations were greatly enriched by anthropogenic activities on military training lands in the lower catchment, firing ranges in particular. Barium, Sr, and Zn also appear to be enriched in the lower part of the catchment, possibly from anthropogenic activities including military activity and roads. Although soils in the catchment are not highly contaminated, isolated areas with high concentrations of Cu, Pb and Sb may warrant management attention given the sensitive nature of the urban forest, which includes the last remaining fresh water swamp forest in Singapore.

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.

Pharmaceutically active compounds and endocrine disrupting chemicals in water, sediments and mollusks in mangrove ecosystems from Singapore.

This study investigated the occurrence of bisphenol A (BPA), atrazine and selected pharmaceutically active compounds (PhACs) in mangrove habitats in Singapore in 2012-2013, using multiple tools (sediment sampling, POCIS and filter feeder molluscs). Using POCIS, the same suite of contaminants (atrazine, BPA and eleven PhACs) was detected in mangrove waters in 28-days deployments in both 2012 and 2013. POCIS concentrations ranged from pg/L to µg/L. Caffeine, BPA, carbamazepine, E1, triclosan, sulfamerazine, sulfamethazine, and lincomycin were also detected in mangrove sediments from the low pg/g dw (e.g. carbamazepine) to ng/g dw (e.g. BPA). The detection of caffeine, carbamazepine, BPA, sulfamethoxazole or lincomycin in bivalve tissues also showed that these chemicals are bioavailable in the mangrove habitat. Since there are some indications that some pharmaceutically active substances may be biologically active in the low ppb range in marine species, further assessment should be completed based on ecotoxicological data specific to mangrove species.

Direct injection of tissue extracts in liquid chromatography/tandem mass spectrometry for the determination of pharmaceuticals and other contaminants of emerging concern in mollusks.

In the present study, a straightforward approach was validated for the analysis of pharmaceutically active compounds and endocrine-disrupting chemicals in the mollusk tissues, with a focus on two species commonly consumed in Southeast Asia (green mussels: Perna viridis; lokan clams: Polymesoda expansa). This approach relied on a simple solvent extraction (shaker table) followed by direct injection in liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). This "cleanup-free" approach was made possible by the use of isotopically labeled surrogates (to correct for matrix effects) and a post-column switch on the LC-MS/MS system (to remove potential interfering material). Altogether, relative recoveries were satisfactory for 36 out of 44 compounds (26-163% range) and excellent for 27 out of 44 compounds (79-107% range). Method detection limits (MDLs) were usually expressed in the nanogram per gram wet weight (ww) range and below. The method was successfully applied to 16 batches of green mussel samples collected in Singapore coastal waters. Trace levels of six compounds were detected in mussel tissues: caffeine (0.22-1.55 ng g(-1) ww), carbamazepine (