Maui's dolphin toxicology research
In 2009, DOC contracted Massey University to do some research into the levels of pollution found in Maui's and Hector's dolphins. This involved testing samples from Maui's and Hector's dolphins that had either washed up or been caught in fishing nets in the previous few years (all the Maui's dolphins had washed up).
The researchers were looking particularly for pesticides like DDT and organochlorines. Dolphins like Maui's and Hector's are particularly at risk because they live in coastal waters where these pesticides end up after being washed down rivers and other waterways.
Maui's dolphin
Relatively high levels of these chemicals were found in both Maui's and Hector's dolphins. However, none of the dolphins examined had concentrations of chemicals high enough to cause a reduction in fertility or a reduction in their immunity. The levels were certainly not high enough to cause death.
There are other pollutants in the environment which could potentially be having an impact, but at this stage it seems unlikely that they are a major cause of decline in the dolphins.