Usually the MHWESG repeats the same surveys over multiple years to create a timeline of surveillance data relevant to the environmental health of the Milford Haven Waterway. In October 2023, the MWHESG embarked on a ‘one-off’ project which remarkably can do the same thing.

The British Geological Society (BGS) were contracted to collect multiple cores from areas of soft mud. They are going to use isotope dating techniques to determine when layers of mud in the cores were deposited. As certain contaminants bind themselves to fine mud particles, levels of contaminants associated with the dated layers of mud are also going to be measured by the BGS through a series of laboratory analyses, thus providing a timeline of contaminant data for the Milford Haven Waterway.

Dr Chris Vane and Dr Andy Marriott spent 4 days in Pembrokeshire taking cores of soft mud on shores most likely to have a net build-up of mud over the decades and not to have been physically disturbed. Sites where cores were gathered include Little Milford, Boulston, Garron Pill, Mill Bay, Cosheston Pill, Pembroke River, Martin’s Haven (Pwllchrochan Flats) and Angle Bay.

Concentrations of the following are to be measured at multiple depths along the core depth:

• Metals, including Mercury
• Organotin compounds
• Hydrocarbons
• Polybrominated diphenyl ethers (PBDEs)
• Polyaromatic Hydrocarbons (PAHs)
• Polychlorinated Biphenyls (PCBs)
• Pesticides

As well as contaminant analyses, the cores are also going to be analysed for various surrogate measurements that will hopefully provide an insight into siltation and nutrient input rates to the estuary over the decades.

The dating of the cores takes time, as well as the many different analyses. Final outputs from the BGS are not expected until March 2025.