Environmental health risk assessment of nickel contamination of drinking water in a country town in NSW

Sampleton (not the real name) is a small country town in rural New South Wales (NSW). Until 2001, the inhabitants of the town had been supplied with drinking water sourced from a local surface water catchment. In 2002, the drought prompted the local authority to negotiate with a local colliery to release its extracted underground mining water into the local drinking water catchment. The local government authority (LGA) treated the water before supplying it as drinking water to its residents.

Between 2002 and 2005, the water samples at Sampleton recorded on the NSW Health Drinking Water Database intermittently exceeded the Australian Drinking Water Guidelines (ADWG) value for nickel of 0.02 mg/L.^1,2 The aim of this risk assessment was to assess the potential health risks associated with the consumption of drinking water with an elevated nickel concentration.

We used the enHealth Guidelines for Assessing Human Health Risks from Environmental Hazards (2002) as the risk assessment tool.³ The ADWG and the WHO guidelines for nickel were used for the specific guidelines on nickel levels in drinking water.^2,4 Chemical analysis of water samples were undertaken by a laboratory accredited by the National Association of Testing Authorities (NATA).⁵ Laboratory test results for nickel in the water samples were compared with the ADWG and the WHO guidelines.

Ground water can contain dissolved metals including nickel (Ni) and chemicals naturally released from rock and soil, which can be harmful to humans.⁶ The estimated average daily dietary intake of nickel is between 0.1 mg/day and 0.3 mg/day.^7,8 The intake of nickel from food is estimated to be less than 0.2 mg/day. Drinking water generally contributes 5–25 μg of nickel per day, which is approximately 2–11% of the total daily oral intake of nickel.⁴ In Australia, the concentration of nickel in typical drinking water is less than 0.01 mg/L with the highest allowable value of 0.02 mg/L.⁹

Non-occupational sources of nickel exposure include food, air and water, but the amount of nickel found is usually much smaller than that typically found in occupational settings.¹⁰ The primary source of nickel in drinking water is from metal pipes and fittings in contact with drinking water. Nickel concentrations in ground water are influenced by soil type, pH level and sampling depth.⁴ Higher concentrations have been reported where drinking water is contaminated with nickel waste discharge from chemical, industrial or mining plants.⁹

The adverse health effects of nickel for humans depend upon the route of administration, water solubility (absorption) of nickel compounds, dose, bodyweight, sensitivity and duration of exposure.^4,11–13 Dermal exposure is the commonest cause of skin irritation to those allergic to nickel, with more females than males being affected.¹⁴ The main adverse effect for this risk assessment is nickel allergic dermatitis, as it occurs at very low levels of exposure. The Expert Group on Vitamins and Minerals estimated that approximately 7–10% of the population in the United Kingdom, predominantly women, have this condition.¹⁵ Allergic contact dermatitis due to nickel sensitivity increases with age and may affect as much as 4–5% of the paediatric population.^16–18 While for some people the reactions are limited to a minor skin irritation, for certain sensitised people the exposure to elevated nickel may cause or aggravate dermatitis. In about half of the sensitive people with vesicular hand eczema, the reactions can be very severe and can lead to loss of working ability.¹⁵

Assessing the dose–response relationship in terms of nickel sensitivity is complex. Christensen and Lagesson observed wide variations in nickel concentrations in blood and nickel excretion in urine in healthy humans when equal amounts of nickel were ingested.⁷ Such variation in sensitivity makes it difficult to estimate the true dose–response effect because a very small exposure to nickel may trigger a rapid response in some people due to their high level of sensitivity. The lowest observed adverse effect level (LOAEL) for an oral dose is reported to be 0.05 mg/kg bodyweight per day when skin is not sensitised.⁸ But when the skin is sensitised, an oral intake of 0.012 mg/kg bodyweight per day may provoke contact dermatitis.¹³

In Sampleton, the mean nickel concentration in drinking water found in water samples taken between January 2002 and December 2005 was 0.03 mg/L (95% CI: 0.02–0.04) (Figure 1).

The high concentration of nickel appears to be a result of the introduction of mine water into the drinking water catchment and the reduction of the natural flow rate within the catchment due to the drought. The lowered flow rate in the catchment due to drought conditions was the main reason that the mine water was accessed to supplement the drinking water supply. The changes in nickel concentrations over the 3-year period could be attributed to changes in natural dilution and the level of demand of water sourced from the colliery to meet the supply requirements.¹⁹

The human health risk of nickel contamination of drinking water in Sampleton has been characterised in consideration of the following two guidelines:

Although the risk assessment found no obvious threat to the health of Sampleton residents, the LGA has been informed of the need to continue to monitor the water supply for nickel levels. The Council was advised that, under the NSW Health Drinking Water Monitoring Program, monitoring of the quality of drinking water should rotate between designated sample sites throughout the distribution system and over time.¹

An enhanced surveillance of the chemical concentrations in the town water supply system has been recommended while mine water is being directed to the drinking water catchment. The use of alternative sources to supplement drinking water supplies during drought conditions, such as mine water in this case, may become more common in rural and regional towns as the drought conditions and water supply levels continue to fluctuate. While this risk assessment provides some reassurance that small increases in nickel in this town water supply are not a hazard to human health, the study does highlight the need for continued vigilance in relation to water quality when water scarcity forces supply authorities to choose alternative sources.