Toxic metals on rise in inner harbours

Metal pollutants could harm tiny worms and bugs that form the building blocks of the marine food chain. Photo / Greg Bowker

Shellfish planted to test contamination levels in Auckland's inner harbours have revealed rising levels of toxic metals.

The Auckland Regional Council says heavy metals are not yet at worrying levels but has warned that rising contamination could hint at problems to come.

Officers put filter-feeding shellfish in harbour sediment to absorb zinc and other pollutants that flow from city roads. The shellfish are then removed and tested.

In a report released yesterday on the state of the Auckland environment, the council said zinc levels rose between 1998 and 2007, while lead levels dropped after it was removed from petrol.

Zinc washes into harbours from car tyres on city roads, among other places.

"We are saying we don't have a problem at the moment [with heavy metals] but the monitoring programme shows we will have a problem if we carry on as we are," said monitoring and research manager Grant Barnes.

The report also showed pollutants from everyday items such as flame retardant and personal hygiene products were ending up in estuaries.

"These emerging chemicals are a cause for concern but at this stage their effects are relatively unknown," said the report.

Mr Barnes said the harbours with rising zinc levels were not popular for shellfish gathering. But metal pollutants could harm tiny worms and bugs that form the building blocks of the marine food chain. That could affect fish, such as snapper, that feed higher up the chain.

He said signs of heavy metal accumulation were found mainly in inner estuaries and tidal creeks such as Tamaki Estuary, Henderson Creek, Mangere inlet and Pahurehure inlet. Heavy metal contamination levels are too low to be picked up by direct testing.

Mr Barnes said that outside urban areas Auckland's marine ecosystems were healthy - although some of the region's almost pristine environments, like Mahurangi Harbour and southeast Kaipara Harbour, were starting to show signs of stress.

Safety of shellfish for human consumption is monitored by the Food Safety Authority, which issues warnings if it has any concerns.