High levels of mercury and arsenic can be spreaded to fish and shellfish in the area of Rotorua.
Gathering and eating wild kai, like koura (crayfish), watercress, tuna (eel), and more recently trout, has long been a part of tikanga (custom) for Te Arawa people. But a recent collaborative study between NIWA and the Te Arawa Lakes Trust has found that toxicants in those traditional foods could pose a risk to people's health.
Rotorua’s geothermal activity imparts high levels of naturally-occurring metals, such as mercury and arsenic, to fish and shellfish caught in the area. The rohe (region) is also affected by other toxicants, like pesticides from agriculture and metals in stormwater. The combined risk of consuming food affected by these toxicants hasn’t been looked at before.
“This study is novel both because it looked at sites and food species particularly relevant to the local iwi, and because it looked at the combined effects of a number of toxicants," says Project Leader Dr Ngaire Phillips.
The study team sampled kai and sediment samples at up to 14 sites, which were tested for metals, as well as organochlorine pesticides like DDT.
Survey results showed that fish harvested from the wild makes up only a small fraction (13 percent) of fish eaten by Te Arawa iwi members, though their overall fish consumption was three times 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 trout was randomly gathered across these sites, there was an increased risk to people’s health from eating it.
A consumption limit of less than one meal per month was recommended for trout, based on median contaminant levels. The survey group were eating more than one meal of trout per month, indicating their health could be at risk. Mercury was generally the main toxicant associated with this risk.
Current consumption rates for pipi, mussels, and watercress also exceed recommended safe levels, but it is important to note that these findings are based on only one site sample. The risks associated with consumption also need to be compared with the health benefits of eating fish, shellfish and green vegetables.
“The mercury results are in line with current guidelines for sensitive populations (infants and pregnant women)”, says John Reeve, Principal Advisor, Toxicology for Ministry of Agriculture and Forestry (MAF). “Also, we have an active education programme around watercress consumption by iwi from geothermal areas. Outside of these areas watercress arsenic levels are very low.”
In contrast, recommended safe consumption limits for koura, eel, smelt, whitebait and kakahi (freshwater mussels) were higher than current consumption levels.
Editor's Note: Original news release can be found here.