May 28, 2000
By JOHN DILLON Staff Writer
The federal government has concluded that the tiny crystalline rock particles found in granite dust can cause lung cancer, a finding that may lead to stricter regulation of Vermont's stone industry.
The National Toxicology Program earlier this month listed crystalline silica dust - a by-product of mining, quarrying, foundry work and stone processing - as a "known human carcinogen."
The NTP, a division of the Department of Health and Human Services, cited studies that found elevated lung cancer rates among those working with stone and other products made from quartz or sand. The findings were published in the government's ninth annual report on carcinogens.
"The link between human lung cancer and exposure to (respiratory crystalline silica) is strongest in studies of quarry and granite workers, and workers involved in ceramic, pottery, refractory brick and diatomaceous earth industries," the report said.
The same annual report also removed the artificial sweetener saccharin from the list of carcinogens and added 14 substances as known carcinogens, including second-hand tobacco smoke and cadmium, a heavy metal used in batteries and other products.
The report upgraded crystalline silica - such as the quartz dust caused by the granite industry - from a suspected carcinogen to a known cancer-causing agent. The document, prepared by the National Institute for Environmental Health Sciences for the National Toxicology Program, cited both human health studies and experiments on laboratory animals as evidence the rock dust causes lung cancer.
Those working in the stone trades are at risk, according to the report. "Granite and stone industry and construction personnel are potentially exposed to respirable silica," the report said.
The national Occupational Safety and Health Administration (OSHA) is using the studies that indicate a silica-cancer link as it develops new worker-safety standards for the granite industry and other occupations, said William Perry, deputy director for health standards at OSHA. Vermont uses the federal OSHA standards for its workplace safety rules.
"We think the evidence is pretty clear there is increased lung cancer risk for exposure to crystalline silica," Perry said Friday.
However, a leading researcher on the health of Vermont granite workers strongly disputes the federal government's conclusion. Dr. William Graham, a retired University of Vermont College of Medicine professor and pulmonary health specialist, has conducted long-term health studies of Barre granite workers. His research has tracked the ravages of silicosis, a deadly, lung-scarring disease caused by breathing granite dust. But Graham said that silica from granite dust is not a likely human carcinogen.
Graham said that while workers employed in the stone sheds have experienced higher than normal lung cancer rates, the disease was likely due to cigarette smoking rather than exposure to the tiny rock particles. Graham, who is preparing a new study for publication, has looked at lung cancer death rates among workers employed prior to 1940 - before controls were put in place to reduce dust - and at the lung cancer deaths among workers employed after 1940. The rates were not substantially different. Yet if granite dust led to lung cancer, the death rate among those employed prior to 1940 - when exposure was at least 10 times greater - should have been much higher, he said.
"The data is not convincing," he said. "If you're going to make a determination like that, I think you should be utterly convinced on scientific grounds."
Should stone workers be worried about getting lung cancer from rock dust? "My impression is definitely not," Graham said. "The only thing they should worry about is whether they are a smoker or not."
The new OSHA safety regulations will be out for public comment next fall. But a spokesman for the Barre granite industry said local companies have already made huge progress in limiting worker exposure to rock dust.
John Castaldo, executive director of the Barre Granite Association, an industry trade group, said silicosis has virtually vanished among those working in the Vermont stone trades. OSHA needs to look at what companies have already done to reduce worker exposure, he said. "There is always the potential for (new) guidelines to have an impact on the industry. But I think the industry has addressed this issue enough so any impact will be minimal," he said.
Officials at OMYA, Inc., which operates a marble-grinding plant in Pittsford, are also concerned about potential new standards covering silica. OMYA referred questions to the Associated Industries of Vermont, a trade group following the issue. AIV Vice President Kerrick Johnson said any industry that uses crushed stone, sand or silica-containing minerals could be affected by new controls on silica dust.
"There has not been consensus within the scientific community" about whether silica can cause cancer, Johnson said. As individual states have drafted air quality regulations, some have found that silica is not a cancer threat, he said. "There's been continual debate. California, Michigan and North Carolina have concluded it was not a carcinogen."
While the studies linking silica to cancer are relatively new, the ubiquitous, abrasive substance has been a health hazard for millennia. An OSHA official said autopsies of mummies unearthed from Egyptian tombs found signs of silicosis. "This is one of the oldest known occupational hazards," said Perry, the OSHA deputy director for health standards.
Twelve percent of the Earth's crust is crystalline silica. The substance - the most common of all minerals - occurs as quartz, sand, agates, and in every geologic strata. People aren't going to inhale silica from a day at the beach. The substance is dangerous only from prolonged exposure to minute particles that lodge deep in the lungs.
The granite industry has taken steps to reduce the hazard by using high-powered vacuum devices to suck the dust from work areas and by requiring workers who use sandblasting equipment to wear respirators, said Castaldo of the BGA.
Before the safety equipment was installed, Barre granite workers in the early part of the century were plagued by silicosis. Men would often die in their 40s from the disease or from the tuberculosis that attacked their weakened lungs. One street in Barre was known by the Italian immigrant stone cutters as la strade delle vedove, the street of widows. "Three-quarters of the people working in the granite industry who were hired before 1940 died of TB or silicosis," Graham said.
The new federal report listing silica dust as a carcinogen says the lung scarring caused by the sharp, minute crystals - which cause silicosis - can also lead to cellular changes and cancer.
Barre City and Barre Town, along with Washington County, have higher rates of lung cancer than the state as a whole, according to state Department of Health statistics.
The male lung cancer incidence in Washington County was 93.5 cases of the disease per 100,000 people for the years 1994-1996, compared to the statewide incidence of 83.7 per 100,000. Both rates are statistically higher than the overall U.S. incidence of 71.7 cases per 100,000, according to the Health Department. Lung cancer kills more men each year than any other cancer.
Graham's latest research has found that Barre stone shed workers also experienced higher-than-expected rates of lung cancer. His study looked at 1,976 workers hired both before and after 1940, the year the industry implemented strict dust control measures. Of those hired before 1940, 81 died of lung cancer, a statistically higher rate than would be expected from the general population. In the group hired after 1940, 100 people died of lung cancer, a rate that is also higher than expected, Graham said.
"Both (of those) rates are excessive. Both are high values statistically," he said.
But Graham said when he examined the health history of those who died, he found that every one was a cigarette smoker. And the death rate in the two groups was not significantly different, despite the vastly different levels of exposure to the rock dust, he said.
Epidemiologists and medical researchers try to tease out what they call "confounding" factors - health histories or other potential causes - when they examine disease rates in a population. Graham said that the research he has seen on the silica-cancer connection has not addressed the confounding impact of smoking.
The International Agency for Research on Cancer, an advisory panel of health experts based in Lyons, France, has also classified crystalline silica as a human carcinogen, citing studies that include Graham's own work. Graham said his research was misinterpreted by IARC, and that much of the research to date has not carefully examined the impact of smoking.
"IARC did in fact conclude it (silica) was a carcinogen, based on studies they said were relatively free of confounding data. I don't think they considered the smoking issue," he said. "A lot of people feel that way."
But OSHA officials said they have considered almost 100 human health studies - including those on granite workers - many of which account for cigarette smoking and other confounding factors.
"We've been primarily focusing on studies where we can account for these confounders and their effects," said Loretta Schuman, OSHA's project leader for the silica rulemaking. "There are a number of studies, where you can account for all other factors, and silica still seems to be a cause (of cancer).