July 25, 2011

Environment Canterbury’s investigations into allegations that agricultural chemicals may have been buried under the Opuha Dam, South Canterbury, during its construction have not raised health or recreation concerns

Earlier sonar studies failed to find any evidence of buried drums in particular areas of Lake Opuha. Interviews with local people had also failed to confirm the reports carried by “Straight Furrow” a month ago

This week, the report on analysis of water, fish (including eels) and sediment samples sent to the Cawthron Institute for review has been received. In summary:

• There were no pesticides found in any of the water samples.
• Pesticide levels in sediment and fish/eel flesh and liver samples were consistent with other samples taken around Canterbury.
• There was no evidence of a new source of contaminant.
• Neither the fish, sediment or water data from Lake Opuha supported the claim that there were extra sources of organo-chorine pesticides in Lake Opuha.
• Cawthron recommends another round of sampling within the next 10 months, to see if there are any trends (upwards or downwards) on pesticide levels in the same location, and also in a separate, comparative catchment.

Tim Davie, Environment Canterbury Manager surface water and ecosystems, said the report provided assurance for recreational users and people who fished Lake Opuha that there was no risk from water contact in terms of pesticide exposure. “Other samples showing pesticide residues were at similar levels to other parts of Canterbury where DDT had been used extensively in the past,” he said.

“Given the legacy of this chemical’s use in Canterbury and New Zealand, these results are not unexpected or unusual. Canterbury was a heavy user of DDT and residues remain in many soils across the region,” he said.

Details from the Cawthron report:
Of the organo-chlorine pesticides (OCPs) analysed from Lake Opuha samples, only DDE, the breakdown product of DDT, a common pesticide used in the past worldwide, and dieldrin, a sheep dip also no longer used, were detected, at levels that could be interpreted as low risk.

The DDE values from Lake Opuha were very similar to the levels reported in the MfE study
(Buckland et al. 1998a,b) and in fish from South Canterbury (Stewart et al. 2011), suggesting that DDE is still present in the Canterbury environment where there has been
historical use of OCPs, but any trend is unclear.

Trout and eel organ samples had similar levels of DDE which is unusual as eels have the potential to live longer and therefore accumulate more contaminants as demonstrated in other studies (Buckland et al. 1998b; Stewart et al. 2011). Trout organs had higher DDE levels than carcasses which could indicate recent exposure. The presence of DDE residues in tissue and sediment samples without the parent DDT suggests a legacy source. Also, dieldrin was only found in fish organ samples and not in the sediments. Therefore neither the fish, sediment or water data from Lake Opuha support the claim that there are new sources of OCPs in Lake Opuha.

ENDS

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