University of Waikato Professor Chris Battershill says the true environmental impact of the dispersants used during the Rena oil spill should be known by Christmas.

The Rena ran aground on the Astrolabe Reef in October and leaked about 350 tonnes of crude oil into the ocean.

Dispersant was used to try and break down the oil slick emanating from Rena.

Dispersants were used to help break up the oil before it washed ashore, but the action was criticised by some scientists.

'This is the first big oil spill in New Zealand's history,” says Chris, 'and we've quickly realised what isn't known in this country about oil dispersants and toxicology.”

Dispersants are chemicals put on an oil spill and work a bit like dishwashing detergent on grease by breaking down the slick into millions of tiny oil droplets.

'Unfortunately, we know little about the toxicology of the dispersants on New Zealand species.

'Right now we need to learn more about the coastline and the food chain implications.”

During the spill, more than 20,000 birds are thought to have been injured or killed and studies are still being conducted into the impact on underwater ecology.

'The relevance of dispersant toxicology on New Zealand species is a huge gap in our knowledge.

'We are using similar dispersants used in the Gulf of Mexico disaster and are in the dark as to the short-term lethal effects versus the long-term effects on the food chain and ecology.

'It's the unknowns that are the big problem now for New Zealand,” says Chris.

Research conducted by the university's Coastal Marine Group in the wake of the Rena disaster is aiming to determine how future marine disasters should be managed.

'The spill globally isn't much, but because of the pristine coastline we have here, and the iwi and community's cultural connection to the coast, the impact is significant.

'By Christmas we will know what the degree of impact is and the scenario for cleaning it up.”

Coastal Marine Group doctoral students are researching aspects of Tauranga harbour and summer research scholarship students have realigned their work to examine the impacts of the Rena spill.

Chris says the university will soon have a clearer picture of how long the marine environment will take to recover, following results of chemistry studies of samples. These were taken during initial response surveys two days after the Rena ran aground and the weeks that followed.

The information has added to data gathered by local councils over the last 20 years and builds a good picture of marine habitats prior to any oil being spilled.

'Having this accurate data to hand is a rare circumstance globally.

'In most other cases of oil pollution it has been difficult to quantify the extent of impact and even harder to determine when the ecology will get back to normal, as elsewhere there is little or no ‘before impact' information making it difficult to know what ‘normal' is.”