Wild kai survey highlights risks of legacy contaminants

Wild kai such as eel (tuna), lamprey (kanakana) and whitebait are a significant cultural, recreational and economic resource for Māori in South Canterbury.

But eating some of these species can pose a risk when they are contaminated by legacy contaminants such as DDT, PCBs and dieldrin, which remain in the environment for a long time and accumulate in the food chain.

A recent collaborative study between NIWA and Te Rūnanga o Arowhenua aimed to assess the current level of contaminants, such as pesticides and heavy metals, in a range of kai species and whether these posed a risk to local Māori, for whom wild kai is an important supplement to their diet.

“This study is novel because we’ve used kai consumption rates for local iwi members, rather than national averages for fish and vegetable consumption. We did this because we thought wild kai consumption rates would be higher than average in some Māori communities" says Project Leader Dr Ngaire Phillips.

“It also adds significantly to our knowledge of contaminants in sediment and kai species from this poorly studied region.”

What the team found, in fact, was that wild kai only forms a small proportion of their diet.

Survey results showed that fish harvested from the wild makes up only a small fraction (13 per cent) of fish eaten by Arowhenua members, though their overall fish consumption was slightly higher than the national average.

Established procedures were used to assess both cancer and non-cancer health risks for iwi members from eating chemically contaminated kai over their lifetimes. The NIWA team found that if kai was randomly gathered from any of the sites tested, there was no increased risk from eating eel, trout, flounder or watercress.

On the other hand, if only the most contaminated kai was consumed, then there was an increased risk to people’s health from eating it. In this instance, a consumption limit of around one meal every three months was recommended for eel, once a month for trout and twice a month for flounder. For eel, the survey group was eating almost one meal per month, exceeding the consumption limit and indicating a risk. DDE, dieldrin and PCBs were the toxicants associated with this risk.

In contrast, recommended safe consumption limits for trout, flounder and watercress were higher than current consumption levels.

Site-specific consumption limits were also derived for each species. Sites of particular concern for eel harvesting were Doncaster (Washdyke Creek), Ohapi Creek and Winchester, where eel consumption should be limited to less than one meal per month. Consumption of trout caught in the Opihi River mouth should also be limited to less than one meal per month.

Dr Phillips says “Our results are preliminary and further work is needed. However, we now have consumption guidelines that can be used by Arowhenua to make informed choices around kai harvesting and consumption. We’ve also provided a sound basis for identifying sites requiring restoration.”