Dr Belinda Cridge (ESR); John McAndrew (Dunedin City Council); Rosemarie Nelson (Tasman District Council)
On the 2nd of February 2021, a “Do Not Drink” notice (DNDN) was put in place for the communities of Waikouaiti, Karitane and Hawksbury Village due to elevated lead readings in the drinking-water supply. That notice was to remain until 28th of July, during which time a comprehensive screening of blood lead levels in the communities was undertaken. This paper provides a brief summary of the events in Waikouaiti and discusses the limitations of Maximum Acceptable Values (MAV) when faced with potential short term, intermittent chemical exposures. The emerging science around lead toxicity is also outlined to highlight why managing lead exposure continues to be important.
As part of a water sampling programme, outside of routine compliance sampling, the Dunedin City Council (DCC) detected elevated lead levels in drinking-water from the Waikouaiti Golf Course. The first elevated result was returned in July 2020. Samples continued to be taken over the next six months and a further 6 samples from various supply-side sites showed evidence of elevated lead. Then in January 0.05 g/m3 (mg/L) total lead was detected in the raw water reservoir exceeding the MAV for drinking water of 0.01 mg/L. Immediately a DNDN was put in place and a community blood lead level screening programme was initiated. All residents were invited to participate and within a four-week period over 1500 people had taken part. Interestingly, very few blood levels were detected above the threshold limit and there was no apparent difference between those who drank from the Waikouaiti supply and those who didn’t. Following an extensive investigation, the DCC found that there is no widespread lead in the drinking water network.
Lead accumulates in the body over time and experts have suggested there may be no safe level of exposure. The MAV for lead in New Zealand aligns with the World Health Organization recommendations. The neurological (brain) effects of lead are the most concerning with exposure in children linked to decreased IQ, behavioural effects, and delayed puberty. In recognition of this in 2021 the New Zealand notifiable blood lead level was decreased from 0.48 µg/L to 0.24 µg/L.
Due to the fact that lead accumulates in the body, determining the risks from multiple short-term exposures is difficult. Most analyses classify acute lead exposure as being constant for three months or more. To model the potential harm from the potential intermittent Waikouaiti exposure, the EPA All Ages Lead Model (AALM) was used. This tool predicted elevations in blood lead levels if the exposure pattern repeated for two years or more. Additionally, new experimental studies suggest that exposure to lead can not only affect the exposed individual but also future generations (children and possibly grandchildren). While these studies are laboratory based, the combined evidence shows that intermittent lead exposure is a potential risk and must be managed appropriately.