Silicosis

What is Silicosis?

Silica, also known as silicon dioxide (SiO2), is made up of a silicon atom and two oxygen atoms, and it is the most abundant mineral on Earth. You can find it in over 95% of rocks and stones.

Breathing in silica dust is one of the earliest known causes of lung disease, going all the way back to 400 BC when Hippocrates linked it to breathing problems in miners. This discovery was furthered in the 1600s, 1700s, and during the industrial revolution. During the 1930s, one of the worst industrial disasters in American history occurred because of this harmful dust. Workers were drilling through a rock in a confined space without proper air ventilation or protection for their lungs. This led to many of them suffering severe lung damage within just a few months due to high exposure to silica dust.

Even today, diseases linked to silica dust continue to be extremely common across the world. Many types of jobs put workers at risk of inhaling dust that contains silica. These include jobs like sandblasting, manufacturing jeans, brickwork, pottery, porcelain work, tunneling, mining, and construction and demolition tasks.

There are two types of silica- amorphous and crystalline. Amorphous silica exists in biological matter like plants, algae, fungi, and also in non-living matter like colloidal sols and powders. This type of silica isn’t harmful. On the other hand, crystalline silica is a type of mineral found in quartz (common in granite and sandstone). Unlike amorphous silica, which has randomly arranged molecules, crystalline silica molecules are fixed in a repeating pattern. This type of silica comes in many forms, with α-quartz being the most harmful to humans.

Particles of crystalline silica can cause health effects if they are small enough to reach the deeper parts of our lungs. These particles, called “respirable crystalline silica” (RCS), are invisible and less than 5 μm in diameter. They are released into the air when silica-containing items are crushed, grinded, or cut. Despite being odorless, colorless, and nonirritating, RCS is classified as a cancer-causing substance by the International Agency for Research on Cancer.

Silica also exists in the form of nanoparticles (SiNPs), which are extremely tiny particles of silicon dioxide measuring less than 100 nm in diameter. They have different characteristics from regular silica. There are two types of SiNPs – solid and mesoporous (the latter has many channels and pores). These silica particles have a number of beneficial properties, like their ability to withstand acid, temperature changes, and organic solvents.

Globally, silicosis, a type of lung disease caused by inhaling respirable crystalline silica, is a major health issue. It results in severe and irreversible lung damage and inflammation, which can be fatal. Although it can be prevented, once contracted, there’s currently no treatment. Silicosis can also make a person more susceptible to other diseases like bronchogenic carcinoma, a type of lung cancer, and autoimmune diseases.

What Causes Silicosis?

Silica comes in a variety of forms and can be used for several different purposes. The Consumer Federation of America and the United States Food and Drug Administration have stated that amorphous silica (a form of silicon dioxide in non-crystalline or glassy form) and salicylates (chemical compounds often used in pain relievers) are safe for us to use when made in larger particles that can’t be inhaled. They are frequently found in products for hair, skin and nails.

Two of the biggest industries making use of silica are the denim and artificial stone industries. For example, denim is often sandblasted with minerals that contain silica to give jeans a worn look. Similarly, artificial stones used for countertops are made of quartz, decorative glass, metal pieces, and a polymer resin, with the crystalline form of silica making up more than 90% of the final stone. However, these processes have led to an increase in the disease silicosis, which is caused by inhaling silica dust.

Another use of silica is in the form of silica nanoparticles (SiNPs) which are minuscule particles that have various uses in cosmetics, food, agriculture and more. For instance, SiNPs are added to processed foods and used in food storage to prevent clumping or foaming of powdered foods, like cake mixes or spices. On top of that, SiNPs can also be used to carry aromas or as a filtering agent. In the future, SiNPs might be used to change certain characteristics of food such as taste, texture, and shelf life or to fortify foods with essential nutrients.

Still, another application of SiNPs is in the healthcare industry, particularly for diagnosing and treating cancer. The unique features of silica particles allow adjustments in the release, solubility, and elimination of drugs. For instance, it’s possible to attach different molecules like organic groups, antibodies or DNA to the surface of the silica. This modification helps the nanoparticles to bind to targeted cells or surfaces, providing longer circulation times and thus making treatments more effective.

SiNPs are also helpful in medical imaging, as they can trap imaging dyes, which are usually not soluble in water, inside the silica matrix. This prevents them from interacting directly with the body’s fluids and increases their stability, making diagnosing diseases less invasive and quicker.

However, research is still ongoing about any potential negative effects of SiNPs. Currently, there is not enough evidence to draw solid conclusions on their toxicity, though it is known that it can depend on different factors like surface modifications, pore size, particle size, exposure route, and dosage.

Risk Factors and Frequency for Silicosis

From 1991 to 1995, over half a million people in China were diagnosed with a lung disease related to silica exposure. Despite the World Health Organization’s goal to eliminate this disease, known as silicosis, by 2030, it still remains a significant health concern worldwide. The major cause of this lung disease is prolonged exposure to silica, which largely depends on how long and intense the exposure is. Most countries regulate workplace silica exposure based on an average over a 40-hour workweek.

Typically, the safe exposure limit of Respirable Crystalline Silica (RCS) is between 0.05 to 0.1 milligrams per cubic meter. However, a study in 2002 found that even workers exposed to the lower limit of 0.05 milligrams per cubic meter for 40 to 45 years were still significantly at risk, with at least one in every 100 workers developing lung disease.

While short-term exposure isn’t generally regulated, even brief periods of high-level exposure can significantly increase the risk of contracting silicosis. The suggested guideline states that the RCS level should never surpass three times the eight-hour average for longer than 30 minutes and should never exceed five times that average.

New industries, such as sandblasting denim and making engineered stone, are seeing alarmingly high rates of silicosis. In the United States, people working with artificial stone countertops are often exposed to dangerous levels of silica dust during the cutting, drilling, grinding, and polishing of stone slabs. One study found that grinding or cutting artificial stone without dust suppression resulted in exposures nearly 300 times the recommended 30-minute limit.

Several studies have also shown a considerable increase in autoimmune diseases in patients with silicosis resulting from occupational exposure to artificial stone dust. Certain smaller industries or hobbies, like ceramics or pottery, can also lead to significant exposure to RCS.

Despite the potential advantages of Silica NanoParticles (SiNPs), not much is known about their possible adverse effects on humans. Some studies showed that SiNPs could trigger inflammation, oxidative stress, and cell death. However, the wide range of physiochemical properties studied might explain the significant variations in toxicity. This field needs more investigation, especially considering the rising production and usage of SiNPs, leading to increased human exposure.

Signs and Symptoms of Silicosis

Silicosis, a lung disease caused by inhaling silica dust, comes in three main forms, each classified by the time between exposure and onset of symptoms. The forms include acute, accelerated, and chronic silicosis, with chronic silicosis being the most common type. This type of silicosis can either be simple or complicated, with the complication known as pulmonary massive fibrosis (PMF).

Every patient with silicosis has a history of exposure to silica dust. Jobs with high exposure to this dust include quartz millers, brick masons, miners, workers who make denim jeans, potters, ceramists, and workers building underground subways and dams. People with silicosis might not show symptoms and could have normal physical check-ups, which is why it’s crucial to consider a person’s occupational history. If symptoms are present, they will depend on the type of silicosis a person has.

• Acute silicosis is rare and typically develops within 5 years of exposure. It commonly occurs in people doing abrasive sandblasting or tunnel work. Patients experience breathing difficulties, chest pain, cough, fever, fatigue, and weight loss, and they often have low oxygen levels.
• Accelerated silicosis develops within 5 to 10 years of exposure and shows symptoms of both acute and chronic silicosis. Patients have rapid growth of lung nodules.
• Chronic silicosis, the most typical type, usually occurs 10 to 30 years after low-intensity, long-term exposure. It’s possible to differentiate between simple and complicated chronic silicosis based on imaging results of the lungs. Patients may be asymptomatic or experience a dry cough or difficulty breathing during physical activity. Complicated chronic silicosis or PMF occurs when lung nodules grow and merge to form larger masses, leading to severe breathing problems, impaired lung function, and increased lung resistance. It can also result in high blood pressure in the lungs and heart conditions.

Only in accelerated or chronic silicosis are swollen lymph nodes found during a physical examination, and they may appear before lung symptoms with lower silica exposure. The build-up of silica dust in the lungs leads to an increased risk of developing lung damage from silicosis.

Testing for Silicosis

One of the diseases that people exposed to rock dust (known as Respirable Crystalline Silica or RCS) might develop is silicosis. There’s no specific lab test to diagnose silicosis. Instead, doctors use a patient’s history of exposure to RCS and certain features seen on imaging tests, like x-rays or CT scans.

The first step in checking for lung diseases related to work environments is usually a chest x-ray. These tests are widely accessible, not too expensive, and they only involve a small amount of radiation. Many people with silicosis do not have symptoms, so the disease is often first spotted on a chest x-ray that was done for other reasons. These x-rays might show small nodules or nodes in the middle and upper areas of the lungs, often with enlarged lymph nodes in the surrounding areas. However, chest x-rays may not be able to pick up early stages of the disease.

High-resolution computed tomography (HRCT), a specific type of CT scan, can be more helpful for spotting the disease in its early stages. People with chronic (long-term) simple silicosis usually have small nodules (less than 10mm in size) that appear in the upper lung areas. Along with the nodules, enlarged lymph nodes might also be seen. For those with chronic complicated silicosis, larger masses can be seen in the back and upper lung areas, which may vary in shape and have irregular edges. These masses can affect the volume of the lungs and distort the windpipe or surrounding areas.

For acute (short-term) silicosis, we only have a few cases to understand how it appears on scans, but some specific features have been observed. These include numerous small nodules all over the lungs along with cloud-like areas known as ground-glass opacities. If additional signs like areas of focussed inflammation and thickening of lung tissue walls are also seen, the patterns on the scans might be referred to as a “crazy-paving” pattern.

The effect of silicosis on lung function can change based on how far the disease has progressed. In the early stages, lung function might not be affected. However, as the disease gets worse, tests may show a decrease in lung volume and the amount of air one can exhale forcefully in one second. Therefore, regular pulmonary function tests are important.

Many countries have set up surveillance programs that perform regular check-ups on workers exposed to RCS. These screenings often include a detailed discussion with a doctor about the patient’s medical history and work environment, a physical exam, relevant imaging studies, and lung function tests. Any worker showing signs of silicosis should be referred to a lung specialist or an occupational health specialist.

Treatment Options for Silicosis

As of now, there is no cure for silicosis, a lung disease caused by breathing in tiny bits of silica, a mineral found in sand, rock, and mineral ores. The standard approach to managing this condition involves providing support to the patient. This could include giving extra oxygen to patients who aren’t getting enough oxygen, giving recommended vaccinations, treating infections promptly, and offering exercises to help improve lung function, which is known as pulmonary rehabilitation.

In the most severe cases of silicosis, where the lungs are severely damaged, a lung transplant may be the only option. However, lung transplants are costly, come with high risks, and are not broadly available. Also, the average survival period after a lung transplant is around 6 to 7 years, so it’s not a permanent solution.

Although there’s no treatment for silicosis once it develops, the disease is entirely preventable. The best way to do this is to reduce exposure to respirable crystalline silica (RCS), tiny particles of silica that can be breathed in and cause silicosis. For those already exposed to silica, early diagnosis of silicosis is vital, as is guidance on how to avoid further exposure to RCS. Quitting smoking is also an important part of managing the disease, as smoking can worsen lung damage caused by silicosis.

As our understanding of how silicosis affects the body improves, new targeted treatments are being considered. These include anti-fibrotic therapy, which slows down the development of scar tissue in the lungs, and anti-cytokine therapy, which suppresses certain substances in the body that can lead to inflammation. However, no large-scale, well-controlled studies have been done to determine the effectiveness and safety of these drugs.

What else can Silicosis be?

For patients suspected to have silicosis (a lung disease caused by breathing in tiny bits of silica), their lung X-rays often look similar to those of other lung illnesses like sarcoidosis, tuberculosis, or even cancer. Therefore, doctors need to rule out these other conditions first. If it’s still unclear whether the person has silicosis, the doctor may decide to take a small sample of lung tissue (a biopsy) for closer examination.

During the microscopic examination of this tissue sample, doctors would look for tell-tale signs of silicosis. This includes whorl-like patterns of a protein called hyaline collagen. They can also detect the presence of silica (the substance that causes silicosis) by using a method called polarized light microscopy which makes the silica crystals visible.

What to expect with Silicosis

Silicosis is a serious, incurable disease that results in permanent scarring of the lungs. This scarring gets worse over time, leading to an unstoppable and often fatal impairment of lung function. This means the lungs can’t perform their job properly, which can end up causing respiratory failure and a condition called cor pulmonale, which is a type of heart failure.

People with silicosis often get infections, both from common and rare types of bacteria called Mycobacteria. The disease can either get worse slowly or quickly, depending on how long and how much a person was exposed to silica. Even if a person stops being exposed to silica completely, the inflammation and damage to the lungs will continue.

Possible Complications When Diagnosed with Silicosis

Exposure to silica and cigarette smoke can notably increase the risk of lung cancer. This connection extends to all types of lung cancer. Studies on animals indicate that the initial inflammation and immune-suppressive environment caused by silica exposure can encourage the growth of cancerous cells in the lungs. Moreover, the progression of a lung disease known as silicosis can often be mistaken for cancer, or it might hide the development of early-stage lung cancers.

One way to differentiate between these conditions is to use imaging techniques. However, CT scans may not effectively distinguish between the two. Magnetic resonance (MR) imaging can be more helpful. For instance, in T2-weighted images, the large clumps of mass found in severely progressed silicosis (PMF) appear as low intensity, whereas cancerous cells display high-intensity signals. Yet, PET scans would not be useful in this case, as both conditions show intense uptake of a substance known as FDG.

Silicosis can also increase the risk of infections, particularly tuberculosis (TB). This is one of the main causes of illness and death in workers exposed to silica, more so in areas with high rates of TB and HIV. The large clumps of mass that are found in severe silicosis can develop cavities in the center, increasing the risk of TB and other related infections. As a result, international guidelines advise proactive treatment for latent TB and TB screening for workers exposed to silica.

Finally, while it is not fully understood, there is evidence that shows exposure to silica can be linked with the development of certain autoimmune diseases. These include conditions like systemic lupus erythematosus, systemic sclerosis (scleroderma), glomerulonephritis, and rheumatoid arthritis.

Potential Health Risks:

• Lung cancer of all types
• Silicosis that may be confused with lung cancer
• Tuberculosis and related infections
• Systemic lupus erythematosus
• Systemic sclerosis (scleroderma)
• Glomerulonephritis
• Rheumatoid arthritis

Preventing Silicosis

Doctors should talk to their patients about how to avoid coming into contact with a substance called respirable crystalline silica (RCS). This is to prevent getting or worsening a disease called silicosis, which can harm your lungs. It’s also important to understand that people who have been around crystalline silica and have smoked cigarettes are at a higher risk of eventually getting lung cancer.