Heat and toxic exposures could harm kidneys in agricultural workers

TUCSON, Ariz. — Heat and constant exposure to toxic metals and metalloids can be a dangerous combination for the kidneys of agricultural workers, a new University of Arizona study found. 

Researchers in the U of A Mel and Enid Zuckerman College of Public Health studied a group of farm workers over a summer and found that high levels of arsenic, cadmium and chromium in the urine were linked to increased signs of kidney injury. They also discovered that greater amounts of uranium in the urine were linked with lower kidney function. The excessive summer heat of the Sonoran Desert worsened the impact of arsenic and cadmium on kidney health.

The results underscore the need for greater attention to the potential health risks to those working in extreme heat environments. They also point to more careful consideration of workplace policies to reduce such risks. A team led by postdoctoral fellow Rietta Wagoner, former doctoral student Nicolas Lopez-Galvez, now at San Diego State University, and Melissa Furlong, assistant professor of environmental health sciences, reported its findings in Environmental Research. 

“We’re seeing an increase in kidney disease in young people who lack typical risk factors, especially in hotter regions,” Wagoner said. “There is evidence that heat, pesticides and metal exposures each play a role, and especially that heat is making potentially toxic exposures worse. Each individually has been studied, but little research has examined a combination of factors. This study is an attempt to answer questions.”

In 2019, Wagoner, Lopez-Galvez and their team studied 77 agricultural workers who traveled seasonally from southern Mexico to a grape farm near the Arizona-Sonora border.  The workers arrived in February and March, at the beginning of the grape season, and stayed until the end of summer. Twenty office workers participated as a comparison group.

The researchers administered surveys, collected daily urine and blood samples, and measured heat stress twice a day with inner ear temperatures and heart rates during the workday and at rest breaks. 

Estimates of kidney function were determined by age, creatinine levels in blood samples, and a marker of kidney injury called urinary neutrophil gelatinase-associated lipocalin, a protein that appears in the kidneys within hours of damage. Metal exposure in the urine and hydration levels were also assessed.

Wagoner and the team measured exposure to potential toxic metals and metalloids such as arsenic, cadmium and uranium while also factoring in the strain of excessive heat on the workers’ bodies. 

“When we looked at heat in combination with metals and metalloids, we found heat especially exacerbated the effects of the metals arsenic and cadmium on the kidney,” Wagoner said. “In other words, together, the effects were worse.” 

When it comes to heat-related illness and kidney injury, prevention is key, Wagoner said.

“We recommend mandatory periodic breaks and rest built into the workday,” she said. “Provide water, electrolyte replacement and have restrooms nearby. Also, allow the workers time to get used to the conditions.”

Wagoner said it is also important to understand the potential sources of metal exposures. She noted that workers drink well water in this region where uranium and arsenic are found in the soil. Cadmium is in cigarettes and alcohol, while lead can be on pottery.

“If we can implement prevention measures early on,” she said, “we can prevent longer term issues.” 

Additional co-authors from the Zuckerman College of Public Health included Paloma Beamer, professor of public health, associate dean of community engagement and member of the BIO5 Institute; Leslie Farland, associate professor of epidemiology; Frank von Hippel, professor of public health and director of the One Health program; Jill de Zapien, program director; and Dr. Cecilia Rosales, professor emeritus and associate dean.

This research was supported in part by the National Institute of Environmental Health Sciences, a division of the National Institutes of Health, under award numbers P30ES006694 and T32ES007091.