Pollution hits shellfish in Bay

Shellfish in Tauranga Harbour and Waihi Estuary are often contaminated with viruses and bacteria to the point where they become unsafe to eat, a study has revealed.
It showed a direct link between causes of pollution such as heavy rainfall or sewage overflows, and unsafe levels of viruses and bacteria in the gut tissue of shellfish collected at six points in the harbour and Waihi Estuary over a year.
Common causes of bacterial and viral contamination included sewage leaks and spills, livestock agriculture, bird populations,  boats, wastewater treatment plants and leaky sewage infrastructure.
Toi Te Ora - Public Health medical officer of health Phil Shoemack said Tauranga Harbour's problems with contaminated shellfish were not uncommon.
"Shellfish harvested close to urban or significant pastoral farming areas are often contaminated," he said.
 "The benefit of this study is we now have direct knowledge of the state of shellfish locally and let people know of the risks."
 
Dr Shoemack said the study gave detailed information on the length of time shellfish remained contaminated following a sewage overflow.
"By testing shellfish after a significant sewage overflow into the harbour, we found it takes three months for the contamination to reduce in shellfish found within 50 metres of the source," Dr Shoemack said.
"For shellfish beyond 50 metres, it was one month before they were safe to eat."
The year-long study was carried out by Toi Te Ora - Public Health, the New Zealand Food Safety Authority, Environment Bay of Plenty (EBOP), Tauranga City Council and Western Bay of Plenty District Council.
New Zealand Food Safety Authority scientists also tested shellfish cooking methods, and found steaming or lightly cooking shellfish was not sufficient to destroy viruses - boiling shellfish for at least three minutes was the only effective method.
 
EBOP had earmarked some communities as areas where more frequent septic tank cleanouts and inspection were required.
These areas included Waihi Estuary, Maketu, Tanners Point, Ongare Point and Te Puna.

EBOP water management group manager Eddie Grogan said the council was keen to undertake further joint studies to pinpoint the exact causes of shellfish contamination and water quality degradation.
Protecting harbours and estuaries and improving the water quality of streams and lakes was expected to be the focus of funding for this year's EBOP Environmental Enhancement Fund.