Oil spilt from the Rena, New Zealand's worst maritime environmental disaster, appears to have mostly dispersed, but more work is needed to determine any long-term environmental impacts, scientists say.
A Waikato University study analysing data collected from more than 30,000 samples, including shellfish, has found levels of polycyclic aromatic hydrocarbons - potent atmospheric pollutants - from Rena's oil has dissipated in most areas of the Bay of Plenty since the disaster just over a year ago.
However, the Rena Recovery Monitoring Programme's chairman, Professor Chris Battershill, says there are still thousands of samples to be analysed over the coming months to get a better understanding of the overall environmental impact.
"We want to be able to get a full picture of how the environment has been affected and pinpoint exactly what impacts are from the Rena grounding," he said.
The recovery programme, which is a one-third complete, involves the monitoring of coastal marine life and offshore reef systems, including the Astrolabe Reef off Tauranga where the remains of the Rena are lodged.
But the Green Party says the government shouldn't take early positive signs as an excuse for inaction on make coastal shipping safer.
Oceans spokesman Gareth Hughes says given the devastating short-term effects the Rena disaster had on the environment and economy, including the deaths of more than 2000 birds, new shipping rules should be put in place to prevent similar disasters.
Rena, a Greece-owned container ship, struck the Astrolabe Reef in October last year.
More than 350 tonnes of oil leaked from the ship and containers and debris that fell overboard washed up along the coastline.