Overview

We recently sought to analyze potential county-level associations between 180 groundwater constituents and kidney cancer incidence in California.¹ Our study, the largest of its kind to date, was based on the long-standing observation that kidney cancer rates vary significantly across different regions, hinting at the potential influence of environmental factors.

Kidney Cancer Incidence Varies Across the World

There are more than 400,000 new cases of kidney cancer globally every year.² These rates vary significantly by continent with North America having the highest age-adjusted incidence rate (12 cases per 100,000 people), followed by western Europe (9.8 per 100,000) and Australia/New Zealand (9.2 per 100,000).³ Our study found that the incidence of kidney cancer varied even within California alone, from 10.5 to 20.5 cases per 100,000 persons in counties with the lowest and highest kidney cancer rates, respectively.

Environmental Exposures (Likely) Matter

Smoking and obesity have been shown to be associated with the development of kidney cancer.^4,5 However, given variation in kidney cancer incidence rates, it is possible that environmental exposures play a role in the development of kidney cancer. Given that groundwater serves as a primary source of water supply for a majority of Californians, we sought to look into the potential association between groundwater constituents and kidney cancer.

The Water-wide Association Study Approach

We adopted a unique approach known as a “water-wide association study” (WWAS), inspired by similar methodologies in genetics. Our WWAS approach aimed to methodically analyze potential associations between 180 constituents present in groundwater and kidney cancer incidence in California. Our method involved 3 cohorts, each encompassing 5 years of groundwater exposure, a 3-year gap, and a 5-year kidney cancer incidence outcomes period.

Groundwater Constituents Associated With Kidney Cancer

Through the WWAS, we identified 13 constituents in groundwater that demonstrated a consistent association with kidney cancer rates. The results revealed 7 constituents that were directly associated with increased kidney cancer incidence: chlordane, dieldrin, 1,2-dichloropropane, 2,4,5-TP, glyphosate, endothall, and carbaryl, many of which are pesticides. Past research has hinted at a possible connection between exposure to certain pesticides and increased kidney cancer risk, corroborating our findings.

Our findings also brought to light 6 constituents that showed an inverse correlation with kidney cancer incidence. That is, these constituents seemed to be associated with lower kidney cancer rates. However, after restricting our cohort to counties with high groundwater use, only constituents positively associated with kidney cancer remained significant.

Study Limitations

Despite these potentially significant discoveries that warrant further study, we acknowledge that our research has limitations. For instance, we used county-level data, which may not account for local variations within the counties. Also, the study’s design didn’t allow us to track individual residential information or consider the possible effect of private well water constituents, which were not included in our data.

Potential Implications of Our Findings

The findings from this study could have implications for public health policy. They underscore the importance of groundwater quality as an environmental factor that could influence kidney cancer rates. Public health efforts to combat kidney cancer, therefore, might consider focusing on reducing exposure to hazardous groundwater constituents.

Further Directions

Our study’s findings suggest the need for further investigation into the identified associations, using patient-level data. Additionally, we encourage similar investigations in other regions, considering that groundwater quality can considerably vary from one place to another.