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DCU researchers discover untreated sewage problems in Dublin Bay area

DCU researchers discover problems around untreated sewage in Dublin Bay area

Dublin City University researchers have discovered legacy issues with untreated sewage and fossil fuel use in the Dublin Bay area. They've also found that the River Liffey is a major carrier of pollutants into seawater.

The researchers have published findings which show that contamination levels from historical sewage disposal in several areas of Dublin Bay have higher than recommended concentrations of chemical compounds left behind by untreated sewage disposal.

The data suggests there are legacy issues when waste is not treated.

Samples were collected on-board the RV Celtic Voyager between the 2nd and 7th of June 2010. Surface sediment samples were collected from 30 stations in Dublin Bay.

The main focus of the study published in the Marine Pollution Bulletin was to determine the distribution and possible sources of Polycyclic Aromatic Hydrocarbons (PAHs) and faecal sterols in Dublin Bay, and whether these man-made pollutants have an impact on microbiological communities on the sea-bed.

Sterols provide a fingerprint for faecal pollution in marine sediments and are used to indicate and determine the source of sewage contamination in the marine environment. Sterols degrade much more slowly once incorporated to sediment.

Although overall levels of faecal sterols in the bay are low in comparison to similar settings the footprint is much higher in areas with a history of untreated sewage release.

Clear evidence of the persistence of sewage residue off the Howth and Dun Laoghaire coasts is presented and points to historical rather than fresh deposition. Although outfall from these points ended in 2001 and 1993 respectively, there is still significant sewage contamination as seen through faecal sterols present in the sediments.

In addition, sewage effluent can alter the cycling of nitrogen and carbon which in turn can influence the potential of microbial communities to biodegrade pollutants from fossil fuels such as PAHs.

The research also investigates carcinogenic organic compounds (PAHs) that linger after the combustion of fossil fuels, from vehicular emissions for example, in sediments in the bay. PAHs linger in certain depositional parts of the bay at higher than recommended concentrations. There are substantial concentrations of PAHs in the sediments of Dublin Bay, with 10 samples exceeding the recommended "effect range" of 552 ng/g.

Above this level PAHs have the potential to cause detrimental biological effects to marine life (biota). The study provides clear evidence that the primary source of PAHs is the combustion of fossil fuels. High levels of PAHs at one station directly influenced by the river Liffey channel, suggests that the river is a main transport route of PAHs to this area of the bay. PAH levels at this station were over five times greater than the warning limit set out by the effect range.

Elevated levels of PAHs were predominantly found in the deeper part of the bay, west of the Burford Bank. This area is of note as the seabed channels formed by the River Liffey flows into this area of the bay. Currents in this deeper area, about 10 km from Dublin Port, are expected to weaken, resulting in a depositional zone for the silt and sediments transported from the River Liffey.

The research was carried out by former PhD student Dr Brian Murphy under the supervision of Dr Brian Kelleher and in collaboration with Xavier Monteys of the Geological Survey of Ireland (GSI).