Australian research has found that just as many workers exposed to occupational respirable crystalline silica have developed autoimmune diseases, in addition to or independent of silicosis.
The Monash University study included 1238 artificial stone benchtop workers who attended screening from June 2019 to August 2023. Nearly one-quarter of men with diagnostic information (253 workers, 24.3%) were diagnosed with silicosis at assessment and surprisingly, the team discovered that detectable antinuclear antibodies were also present in a quarter of the group (24.6%).
Those with elevated levels of RCS exposure were more likely to have detectable ANAs and detectable autoantibodies were found in significantly higher proportions among those diagnosed with silicosis.
According to the lead author, Dr Karen Walker-Bone, while many of the largest studies of autoimmune diseases in RCS-exposed workers have investigated their occurrence among people diagnosed with silicosis, most case–control studies to date have lacked power.
“However, there was evidence that autoantibodies were found, alongside the reduction of immune tolerance, in RCS-exposed workers even in the absence of silicosis, and cases of autoimmune disease have also been reported in engineered stone benchtop industry workers,” she explained.
“Occupational environmental exposures have been implicated in autoimmune diseases with some of the most convincing evidence of the role of respirable crystalline silica exposure for SLE; systemic sclerosis; rheumatoid arthritis and antinuclear cytoplasmic antibody (ANCA)-associated vasculitis.”
Recognisable by the presence of pathogenic autoantibodies and autoreactive T-helper cells directed against host antigens, autoimmune diseases can be single-organ (eg, Grave’s disease) or multisystem (eg, systemic lupus erythematosus (SLE)).
While having detectable autoantibodies was not completely diagnostic of an autoimmune disease, their presence in certain rheumatic diseases, such as SLE and RA, has been shown to predate clinical features often by many years.
Dr Walker-Bone explained that when RCS was inhaled, the body sent in macrophages to try and consume the particles.
“But they are so toxic that they kill those macrophages, leaving the particles behind to cause local inflammation in the lungs – or silicosis. However, the persistence of a foreign body so close to a rich blood supply seems to be precipitating the development of autoantibodies,” she said.
In addition to the 24.6% of workers with ANAs, ENAs were discovered at 4.6% and RF at 2.6% in those without clinically diagnosed autoimmune disease.
The most common autoimmune diagnoses that occurred after RCS exposure were SSc, ANCA-associated vasculitis and RA.
“The prevalence of detectable ANAs in this cohort was much higher than that expected in a general adult male population. For example, among those aged 40–49 years, close to the median age of our cohort, in the US National Health and Nutrition Examination Survey, the prevalence of ANAs was ˂ 6%,” Dr Walker-Bone said.
“Our study indicated the role of very high levels of RCS exposure in autoantibody detection for ANAs. The mechanism for this is not well understood but it is hypothesised that once macrophages ingest silica particles, they are apoptosed by the toxic silica without total removal of the particles, leading to ongoing immune activation.
“Animal studies have also suggested that silica has a dose-dependent adjuvant effect on proinflammatory pathways that can increase the response to an antigen.”
Silica sand is the main structural component in several construction products and other industrial materials to improve durability and structural integrity, and according to WorkSafe Australia, the following materials have been flagged as containing silica:
| Type | Amount of crystalline silica (%) |
| Marble | 2 |
| Limestone | 2 |
| Slate | 25 to 40 |
| Shale | 22 |
| Granite | 20 to 45 (typically 30) |
| Natural sandstone | 70 to 95 |
| Engineered stone | Up to 97 |
| Aggregates, mortar, and concrete | various |
Source: https://www.safeworkaustralia.gov.au/safety-topic/hazards/crystalline-silica-and-silicosis