Nitrate contamination in drinking water and colorectal cancer: Exposure assessment and estimated health burden in New Zealand

Jayne Richards; Tim Chambers; Simon Hales; Mike Joy; Tanja Radu; Alistair Woodward; Alistair Humphrey; Edward Randal; Michael G Baker

doi:10.1016/j.envres.2021.112322

Nitrate contamination in drinking water and colorectal cancer: Exposure assessment and estimated health burden in New Zealand

Environ Res. 2022 Mar;204(Pt C):112322. doi: 10.1016/j.envres.2021.112322. Epub 2021 Nov 2.

Authors

Jayne Richards¹, Tim Chambers², Simon Hales³, Mike Joy⁴, Tanja Radu¹, Alistair Woodward⁵, Alistair Humphrey⁶, Edward Randal³, Michael G Baker³

Affiliations

¹ School of Architecture, Building and Civil Engineering, Loughborough University, Epinal Way, Loughborough, LE11 3TU, UK.
² Health, Environment & Infection Research Unit, Department of Public Health, University of Otago, Wellington, New Zealand. Electronic address: tim.chambers@otago.ac.nz.
³ Health, Environment & Infection Research Unit, Department of Public Health, University of Otago, Wellington, New Zealand.
⁴ School of Government, Victoria University of Wellington, New Zealand.
⁵ Epidemiology & Biostatistics, School of Population Health, University of Auckland, New Zealand.
⁶ Public Health Physician, Christchurch, New Zealand.

PMID: 34740625
DOI: 10.1016/j.envres.2021.112322

Abstract

Background: Epidemiological evidence in multiple jurisdictions has shown an association between nitrate exposure in drinking water and an increased risk of colorectal cancer (CRC).

Objective: We aimed to review the extent of nitrate contamination in New Zealand drinking water and estimate the health and financial burden of nitrate-attributable CRC.

Methods: We collated data on nitrate concentrations in drinking water for an estimated 85% of the New Zealand population (∼4 million people) who were on registered supplies. We estimated nitrate levels for the remaining population (∼600,000 people) based on samples from 371 unregistered (private) supplies. We used the effective rate ratio from previous epidemiological studies to estimate CRC cases and deaths attributable to nitrate in drinking water.

Results: Three-quarters of New Zealanders are on water supplies with less than 1 mg/L NO₃-N. The population weighted average for nitrate exposure for people on registered supplies was 0.49 mg/L NO₃-N with 1.91% (95%CI 0.49, 3.30) of CRC cases attributable to nitrates. This correlates to 49.7 cases per year (95%CI 14.9, 101.5) at a cost of 21.3 million USD (95% 6.4, 43.5 million USD). When combining registered and unregistered supplies, we estimated 3.26% (95%CI 0.84, 5.57) of CRC cases were attributable to nitrates, resulting in 100 cases (95%CI 25.7, 171.3) and 41 deaths (95%CI 10.5, 69.7) at a cost of 43.2 million USD (95%CI 10.9, 73.4).

Conclusion: A substantial minority of New Zealanders are exposed to high or unknown levels of nitrates in their drinking water. Given the international epidemiological studies showing an association between cancer and nitrate ingestion from drinking water, this exposure may cause an important burden of preventable CRC cases, deaths, and economic costs. We consider there is sufficient evidence to justify a review of drinking water standards. Protecting public health adds to the strong environmental arguments to improve water management in New Zealand.

Keywords: Cancer; Exposure assessment; Nitrates; Population attributable fraction; Water.

Publication types

Research Support, Non-U.S. Gov't
Review

MeSH terms

Colorectal Neoplasms* / chemically induced
Colorectal Neoplasms* / epidemiology
Drinking Water*
Humans
New Zealand / epidemiology
Nitrates / analysis
Nitrates / toxicity
Nitrogen Oxides
Water Pollutants, Chemical* / analysis
Water Pollutants, Chemical* / toxicity
Water Supply

Substances

Drinking Water
Nitrates
Nitrogen Oxides
Water Pollutants, Chemical