Silica Dust Hazard

Silica is a naturally occurring mineral in rock and soil. When inhaled, silica dust can cause silicosis, cancer and increases the risk of Tuberculosis (TB) infection. Airborne silica is present in numerous industries including construction, mining, foundry work, glass, concrete manufacturing, painting, pottery, and stone crushing.

Occupational exposure to silica dust in the mining industry is a global concern. The labor force in most developing countries is comprised largely of informal migrant workers and the attrition rates are high. Over one million mineworkers in China and 500,000 in South Africa have been diagnosed with silicosis. In southern Africa migrant workers in mineral mines experience higher rates of HIV and an associated TB incidence that is reportedly ten times that of the general population. India's mining industry provides employment to over 1.3 million people with thousands more employed in small, unofficial mines, but few are ever diagnosed with silica-related disease. The country's Supreme Court ordered states to increase medical surveillance programs to identify cases and to compensate silicosis victims.  However, the implementation of these measures has been inconsistent as most states have done very little.

In much of the developing world excessive exposures to silica dust are common in the stone crushing industry where most mills operate without dust controls. It is estimated there are over 12,000 stone crusher mills in India alone, which provide direct employment to over half a million workers, many of whom are disadvantaged women and children. Studies have shown increased morbidity and mortality among silica exposed workers from silicosis, lung cancer, TB, and other lung diseases.

Growth in Informal Mining

As global demand for minerals and gemstone continues to rise, there has been a shift from formal sector industrial mining to informal mining in more than 85 mostly low and middle-income countries. It is estimated that there are 49.5 million artisanal miners or more than ten times the number employed in industrial mines. Seven of the ten countries with more than one million artisanal miners are in Africa and the rest are in Asia.

As global demand for metals and other minerals is expected to dramatically increase to supply the clean energy transition, it is likely that informal mining will continue to expand. Although artisanal gold mining gets much of the attention, self-employed miners work to mine and process cobalt, lithium, lead, tin, gemstones, diamonds, coal, copper, chromite, manganese, iron ore, bauxite, granite, barite, mica, marble, limestone, sandstones, slate and more. 

Link with Tuberculosis (TB)

Silica exposure has been linked with TB for over a century. Silica exposures in stone crushing mills in India have been shown to increase the risk of acquiring active Tuberculosis (TB) by nearly seven-fold. A study conducted in India of over one hundred former stone crusher workers showed that 48% had TB alone or in combination with silicosis. The risk is not limited to high burden TB countries as a study from Michigan (USA) showed that the individuals with silicosis had a 1,000 times greater incidence of TB than the general population. This link is even more significant as TB is the most common cause of death in those with silicosis.

Reducing exposures to respirable silica in the workplace would lead to a dramatic reduction in TB incidence among exposed populations. There are many other industries with excessive silica dust exposures including mining, ceramic and glass manufacturing, construction, and cement employing at least 230 million workers around the world. Most of the highest exposed individuals work in the informal sector, including more than 49 million artisanal small-scale miners.

Recent studies documenting TB, silicosis and lung disease among ASM demonstrate that silica dust exposures and health outcomes are significantly worse than what we observe in industrial mining.

For example these studies have demonstrated that:

    • In Malawi informal miners 50% more likely to develop TB than industrial miners;

    • Informal miners in Ghana had a 2.5X greater TB prevalence than background levels; and

    • Artisanal miners in Zimbabwe had a 34X greater TB prevalence than background rates in the general population and 19% had silicosis.

The United Nations has recognized the need to establish programs to reduce TB among miners and other vulnerable workers exposed to silica dust. The UN declaration from the first ever General Assembly High-level Meeting on TB held in September 2018 called on countries to commit to “implementing primary prevention in high-risk occupations by reducing silica dust exposures in mining, construction and other dusty workplaces.”  In 2023, the UN highlighted the risks to miners and others exposed to silica in their second TB declaration.

OK International spearheaded this effort at the UN to recognize the need for TB prevention in the workplace. We estimate that 300,000 new TB cases can be prevented each year with appropriate workplace interventions.  Millions of additional cases of silicosis would also be prevented. 

International Silicosis Elimination Goal

The International Labour Organization (ILO) and World Health Organization (WHO) have responded to this public health crisis by launching an International Programme on the Global Elimination of Silicosis in 1995. The objective of the programme is to eliminate silicosis in all countries by 2030. Goals are achieved through international partnerships to raise awareness of the health effects of silica exposure and introduce appropriate technologies to reduce exposures.  However, this effort has failed to attract the funding to adequately sustain this effort. 

India Case Study

As construction and road building is booming in India, small scale stone crusher industries are proliferating throughout the country, often in violation of air pollution and zoning guidelines. Airborne silica generated from these stone crushing mills throughout the Khurda region of Orissa, India are suspected to be the cause of increased morbidity and mortality rates from silicosis, cancer, and other lung disease. Unprotected workers including children working without respirators, proper ventilation, and dust suppression systems are subject to considerable health risks. Dust from these operations is also known to affect local communities. Without adequate screening for early detection of lung disease (virtually none exists), these workers often reach late-stage conditions prior to receiving care, at which point medical treatment is ineffective.

Starting in 2003, OK International formed a partnership with an Indian NGO, Jeevan Rekha Parishad (JRP), based in the State of Orissa to provide technical assistance to help reduce silica emissions from a cluster of stone crusher mills. We provided JRP with donated equipment to evaluate airborne exposures to silica and instructed the organization's volunteers and staff on proper use of the equipment. We then initiated a study to assess airborne silica exposures in stone crushing operations in this area and determined that silica exposures were approximately four times the regulatory level.

With a modest education and outreach efforts, our partners encouraged over 40 mill owners to install water spray systems to reduce silica levels in their operations. The results of this pilot program demonstrate reductions in average respirable silica of 80% after water spray controls were installed. The success of this pilot program suggests that relatively inexpensive modifications currently available in the local market can be effective at reducing silica exposures in stone crushing operations. We are now actively working to take this pilot project to a national level in India.

See our video Reducing Silica Exposures in Stone Crushing.

Silica released from stone crushing is causing an epidemic of silicosis, cancer, other lung diseases and increases the risk of acquiring Tuberculosis (TB). This situation is particularly dire in India where the stone crushing industry employs over half a million people, many of whom are women and children. Occupational Knowledge International (OK International) is providing technical assistance to small-scale stone crushing mills on how to reduce emissions in their operations. This video documents how they reduced silica exposures by over 80% in one pilot study.

http://www.youtube.com/watch?v=6rBSL1WfNgw

For additional information on this project see: Reduction of Respirable Silica Following the Introduction of Water Spray Applications in Indian Stone Crusher Mills, Gottesfeld, P, Nicas, M, Kephart, J, Balakrishnan, K, and Rinehart, R., International Journal of Occupational and Environmental Health, Vol. 14, No. 2, 2008 .

OK International has estimated the public health impact of introducing water spray systems in all stone crusher mills in India. Based on the exposures reductions we observed and epidemiological studies conducted in the U.S. we were able to make some conservative predictions. If this water spray technology were adopted in stone crushing mills throughout India, we estimate that it will prevent at least 90,000 cases of silicosis and 35,000 deaths from cancer and TB.

See our Projects page to learn more about OK International's current silica reduction projects in India and project partners.

Safer Mining Practices Reduce Exposures in Small-scale Mining in Nigeria

A pilot program to reduce lead poisoning in Nigerian gold mining communities has brought extraordinary improvements to an area where hundreds of children had died from lead poisoning. OK International conducted the two-year effort to introduce safer mining practices to artisanal miners that was successful at preventing deaths and reducing lead poisoning in highly exposed villages.

“Our pilot project demonstrated that low-cost dust control measures were effective at reducing average airborne lead exposures by 95 percent,” said Perry Gottesfeld, Executive Director of OK International. The organization partnered with Doctors Without Borders/ Médecins Sans Frontières (MSF) in this effort.

The safer mining project took place in the Shakira community in Niger State, Nigeria where high levels of lead are naturally present in the gold ore. The primary objective was to reduce lead exposures among artisanal small-scale miners and minimize take home exposures to protect children in this area.

“We worked cooperatively with miners to provide them with the information and tools to reduce their exposures to lead and silica dust. Together we showed that these efforts minimized contamination and helped save lives.” Gottesfeld said.

The organization demonstrated the effectiveness of reducing airborne lead levels by working with miners to convert dry operations to wet methods. Water spray misting was proven to be highly effective while minimizing water consumption. In addition to significant reductions in airborne lead, we reported that these control measures reduced the smaller respirable silica dust by 80%. See the full publication Reducing Lead and Silica Dust Exposures in Small-Scale Mining in Northern Nigeria.

Silica dust exposure are common in stone crushing, mining, quarrying and other industries.

Sign displayed at a stone crusher mill to raise awareness of dust hazards among workers.