Godfred Odame Duodu

Potential bioavailability assessment, source apportionment and ecological risk of heavy metals in the sediment of Brisbane River estuary, Australia

A weak acid extraction was used to mobilize the loosely bound metals in estuary sediment samples. More than 30% of Ag, As, Ca, Cd, Co, Cu, Hg, Mn Ni, Pb and Zn were leached from the sediment showing that these metals are significantly present in the bioavailable form. PCA/APCS identified three sources of the metals, namely: lithogenic accounting for 72%, shipping related contributing 15% and traffic related representing 13% of the total load. Application of pollution index (PI) and modified pollution index (MPI) revealed that the sediment range from unpolluted to heavily polluted while ecological risk index (RI) classifies the sediment as posing low ecological risk modified ecological risk index (MRI) suggests considerable to very high ecological risk. To provide holistic insights into the ecological risks posed by metals, enrichment factor, MPI and MRI are recommended for the assessment of sediment in complex environments such as estuaries.

Optimization of in-cell accelerated solvent extraction technique for the determination of organochlorine pesticides in river sediments.

Organochlorine pesticides (OCPs) are ubiquitous environmental contaminants with adverse impacts on aquatic biota, wildlife and human health even at low concentrations. However, conventional methods for their determination in river sediments are resource intensive. This paper presents an approach that is rapid and also reliable for the detection of OCPs. Accelerated Solvent Extraction (ASE) with in-cell silica gel clean-up followed by Triple Quadrupole Gas Chromatograph Mass Spectrometry (GCMS/MS) was used to recover OCPs from sediment samples. Variables such as temperature, solvent ratio, adsorbent mass and extraction cycle were evaluated and optimized for the extraction. With the exception of Aldrin, which was unaffected by any of the variables evaluated, the recovery of OCPs from sediment samples was largely influenced by solvent ratio and adsorbent mass and, to some extent, the number of cycles and temperature. The optimized conditions for OCPs extraction in sediment with good recoveries were determined to be 4 cycles, 4.5 g of silica gel, 105 °C, and 4:3 v/v DCM: hexane mixture. With the exception of two compounds (α-BHC and Aldrin) whose recoveries were low (59.73 and 47.66% respectively), the recovery of the other pesticides were in the range 85.35-117.97% with precision <10% RSD. The method developed significantly reduces sample preparation time, the amount of solvent used, matrix interference, and is highly sensitive and selective.

Factors influencing organochlorine pesticides distribution in the Brisbane River Estuarine sediment, Australia

Sediment samples collected from Brisbane River were analysed for organochlorine pesticide residues (OCPs). The factors influencing OCPs distribution in the sediment were investigated using multivariate analytical tools. Thirteen OCPs were detected in the sediment with concentrations ranging between below detection to 83.9ng/g, and detection frequency >90%. With the exception of dieldrin, the OCP inputs appear to be historical and may cause adverse ecological impacts. Multi-criteria ranking of the factors influencing the OCPs (except dieldrin) distribution in the sediment revealed that TOC>silt>intensive urban land use>population>seasons. Dieldrin distribution is significantly influenced by season>TOC>silt>intensive urban land use>population. The study helps to prioritise factors required for managing OCPs contamination in sediments and identification of appropriate mitigation measures.