An investigation of sea snails on Astrolabe reef has cleared them of any traces of pollution from the tributyltin paint on one of the Rena wreck's antifouling layers.

Sensitive marine life is unaffected by Tbt pollution.

Paint scrapings from the Rena's hull showed some residual traces of Tbt and the study was undertaken by Cawthron Institute scientists to determine if sea life near the wreck has been affected.

Tin based anti-fouling was used on Rena in 1999, and later treated and overpainted. The former containership struck Astrolabe Reef on October 5 2011 and later broke up with the larger stern section of the wreck sliding down the reef into deeper water. While the bow section was cut up and salvaged piece by piece, save for a remnant, the larger stern section lies in water up to 50m deep.

The hearing to determine whether to leave the remainder of the wreck on the reef begins on June 23.

The Cawthron Institute study commissioned by Beca, is based on the fact that levels of Tbt too low to measure directly, can cause female whelks to grow penises.

For the study a number of whelks were collected from Astrolabe Reef and from nearby Okaparu Reef as a control population.

They were transported to Auckland's AIT where they were dissected and the females checked for penises.

The result of the survey showed the females from both groups remain female. There is no measurable effect on the reproductive state of the sensitive whelk species as a result of possible Tbt exposure from the grounding of the Rena.

The report was released to media on Friday afternoon by the Bay of Plenty Regional Council.