Pesticides in snails, water not drinkable

Toxic pesticides are still being found in estuarine mud snails and sediment next to Mapua's former Fruitgrowers Chemical Company site.

Two offsite groundwater bores south of the site also contain water that fails the national drinking water standards and contact with the water should be avoided, says a monitoring report.

A site audit report completed last year confirmed the area was fit for residential, commercial and open-space use, subject to a list of conditions, and recommended the Tasman District Council carry out further sediment, snail, groundwater, soil and ammonia-gas monitoring.

Prior to a $12 million remediation project at the site between 2004 and 2008, elevated concentrations of contaminants in marine sediments next to the site were found.

The contaminants of most concern were organochlorine pesticides which include DDX and aldrin, dieldrin and lindane (ADL).

The Ministry of Health's take on a report released on Monday is that the cleanup of the site had not created long-term health problems. However, many residents remain sceptical.

A monitoring report completed by Davidson Environmental for the council shows only three out of 26 deep marine sediment samples next to the site meet the DDX soil acceptance criteria. Eighteen out of 26 samples for ADL achieved the criteria.

The report said small increases in the pesticides were recorded at some sites which could be related to re-contamination of sediment from the site during remediation and natural movement of marine sediment.

However, the concentrations were "dramatically" lower than those recorded prior to remediation, the report said.

The highest pesticide levels were recorded west of the site.

A peak in snail contamination was also recorded last October, which had DDX readings of six times more than a sample taken in February that year, said council resource scientist Jenny Easton in a report.

"The snails ingest the bacteria and algae from the mud, not from the seawater itself, and we would expect to see a correlation between the organochlorine concentrations in the mud and snail flesh."

Council environmental manager Dennis Bush-King said the snail readings were "unfortunate".

"We don't understand quite how that happened, because the marine sediments are cleaning up and getting down to low levels. We do know that people don't go out there and harvest the snails."

People would have to eat 20 snails a day to be affected, he said.

The council's first annual report of groundwater monitoring showed there were two bores south of the site where the water quality failed drinking water standards.

The report on the bores, by Pattle Delamore Partners, said two offsite bores at Tahi St were contaminated and groundwater beneath the site had been affected by remediation work.

The most commonly occurring chemicals in the groundwater were nitrogen, DDX and ADL.

Mr Bush-King said all properties were connected to the council water reticulation system and people should rely on it.

The groundwater report said an adverse effect of the contamination was seepage on to the beach front.

The concentrations would be diluted by water flow, but could lead to the growth of slime and affect snails and shellfish, the report said. The council has been told to erect signs warning people against collecting shellfish.

- © Fairfax NZ News