Workers at Chinese vinyl window blind factories that use methyltin stabilizing agents are at greater risk of developing kidney stones, according to a new study from American and Chinese researchers.
The study, from the University of Buffalo and three Chinese research institutions, examined several hundred workers in three vinyl factories — two of which used methyltins as heat stabilizers and one that did not as a control group — and said it found correlations between exposure to trimethyltin chloride and kidney stones.
A University of Buffalo statement said researchers are interested in TMT because more people worldwide are developing kidney stones, with the prevalence in the U.S. doubling between 1994 and 2010.
The study reported “statistically significant positive associations” for risk of kidney stones from workplace exposure to TMT, which is a neurotoxin that can form as a byproduct of using other methyltins as heat and light stabilizers in manufacturing PVC products.
The study, which said it is the first to find a link between low-level workplace TMT exposure and kidney stones, also reported that TMT-exposed workers were more likely to have symptoms or positive test results for hypertension, gallstones, low hemoglobin counts and other problems.
One of the study's authors, Xuefeng Ren, an assistant professor in Department of Social and Preventive Medicine at the University of Buffalo, said the study raises questions about the general public's exposure to TMT from PVC pipes.
“There is not enough information available about environmental methyltin exposure, but given the widespread use of PVC pipes in public facilities, homes and workplaces, there is growing concern that methyltins leached from these materials can contaminate drinking water, food and various ecosystems,” he said in a news release from the university.
“We suggest that larger, more comprehensive studies be undertaken to confirm these findings, particularly in members of the general public, who may encounter low levels of TMT and other methyltin compounds through drinking water or other pathways.”
In an email to Plastics News, Ren said chlorinated methyltin compounds are water-soluble and can leach from PVC products. He said studies have detected methyltin compounds in surface water and sediment and PVC pipes could be a source.
Ren declined to release the names of the three factories, but said they are all in Qingyuan.
Researchers said they did clinical examinations that included ultrasonography and blood and urine samples from workers at the end of shifts, along with air samples, interviews and questionnaires. They examined 335 workers, 216 from the two factories using methyltins and 119 from the one that did not.
The study said workers developed kidney stones at much lower exposure levels than the occupational exposure limits for all organotins set by the National Institute for Occupational Safety and Health in the U.S.
Ren said researchers are recommending lower exposure limits for methyltins, which are one kind of organotin.
The role of PVC manufacturing in accounting for TMT's presence in the environment is attracting the attention of researchers in China.
Several studies in the country in recent years have reported evidence of TMT in China's aquatic environment, and researchers are beginning to look at neurotoxicity.
Some studies say PVC plastic manufacturing is a primary source of TMT. A study this year from the Guangdong Medical Laboratory Animal Center reported, for example, that “extensive uses of methyltin compounds in [PVC] production have led to a dramatic increase of occupational-related methyltin poisoning accidents and the widespread contamination of methyltins.”
A 2011 study from researchers at Oregon State University and Wenzhou Medical College said there had been 67 TMT poisoning incidents worldwide between 1978 and 2008, with the most common acute worker exposure coming from plastic manufacturing or processes that require reheating plastic.
In addition to the University of Buffalo, the study of the Qingyuan factories included researchers from the Guangdong Medical Laboratory Animal Center, the Guangdong Poison Control Center and the School of Public Health at Sun Yat-Sen University in Guangzhou.
The study, “Chronic Low-Level Trimethyltin Exposure and the Risk of Developing Nephrolithiasis,” was published in the June 13 issue of the journal Occupational and Environmental Medicine.