River toxicity assessment using molecular biosensors: Heavy metal contamination in the Turag-Balu-Buriganga river systems, Dhaka, Bangladesh

Pollution in rapidly urbanising cities and in delta systems is a serious problem that blights the lives and livelihoods of millions of people, damaging and restricting potable water supply and supplies to industry (Whitehead et al, 2015, 2018). Employing new technology based on luminescent molecular biosensors, the toxicity in the rivers around Dhaka in Bangladesh, namely the Turag, Tongi, Balu and Buriganga, has been assessed. Samples taken at 36 sites during medium and low flow conditions and during the Bishwa Ijtema Festival revealed high levels of cell toxicity, as well as high concentrations of metals, particularly aluminium, cadmium, chromium, iron, zinc, lithium, selenium and nickel. Chemical analysis also revealed low dissolved oxygen levels and anoxic conditions in the rivers at certain sites. The bacterial molecular biosensors were demonstrated to be fast, with results in 30 min, robust and a highly sensitive method for the assessment of water toxicity in the field. Furthermore, the biosensor toxicity analysis correlated with the metals data, and a multivariate regression relationship was developed relating toxicity to key metals, such a selenium, zinc and chromium. The resulting model has been validated against split samples and the Bishwa Ijtema Festival data. The combination of modelling and the molecular biosensor technology provides a new approach to detecting and managing pollution in urban river systems.

Microbial analysis of soil and groundwater from a gasworks site and comparison with a sequenced biological reactive barrier remediation process

AIMS

To investigate the distribution of a polymicrobial community of biodegradative bacteria in (i) soil and groundwater at a former manufactured gas plant (FMGP) site and (ii) in a novel SEquential REactive BARrier (SEREBAR) bioremediation process designed to bioremediate the contaminated groundwater.

METHODS AND RESULTS

Culture-dependent and culture-independent analyses using denaturing gradient gel electrophoresis (DGGE) and polymerase chain reaction (PCR) for the detection of 16S ribosomal RNA gene and naphthalene dioxygenase (NDO) genes of free-living (planktonic groundwater) and attached (soil biofilm) samples from across the site and from the SEREBAR process was applied. Naphthalene arising from groundwater was effectively degraded early in the process and the microbiological analysis indicated a dominant role for Pseudomonas and Comamonas in its degradation. The microbial communities appeared highly complex and diverse across both the sites and in the SEREBAR process. An increased population of naphthalene degraders was associated with naphthalene removal.

CONCLUSION

The distribution of micro-organisms in general and naphthalene degraders across the site was highly heterogeneous. Comparisons made between areas contaminated with polycyclic aromatic hydrocarbons (PAH) and those not contaminated, revealed differences in the microbial community profile. The likelihood of noncultured bacteria being dominant in mediating naphthalene removal was evident.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work further emphasizes the importance of both traditional and molecular-based tools in determining the microbial ecology of contaminated sites and highlights the role of noncultured bacteria in the process.