Over the last 30 years there has been a decline in heavy metal contamination in the Derwent estuary. However by national and international standards the Derwent's heavy metals remain high in water, sediment and living organisms (eg. shellfish).
Heavy metals can be toxic to estuarine and marine mammals, and to humans if ingested through the consumption of seafood.
The Derwent Estuary Program received Commonwealth funding for a Water Quality Improvement Plan for heavy metals and nutrients. The aim of this program was to better understand and further reduce heavy metal contamination in the Derwent estuary.
The major elements of this program included:
- Determining heavy metal inputs and existing levels
- Computer modelling of water and sediment transport processes controlling the movement of heavy metals
- Evaluating the processes that influence heavy metal availability in sediments
- Establishing heavy metal targets and the loads required to achieve these
- Identifying and evaluating management options to meet these targets
- Recommending actions for implementation
Recommended actions include further management of contaminated groundwater and stormwater at the Nyrstar Hobart Smelter, careful management of contaminated sediments and better public information about seafood safety. The Water Quality Improvement Plan also recommended that nutrients be carefully managed to avoid low oxygen conditions that could cause metals to be released from contaminated sediments.
Restoring and promoting the Derwent estuary