Silicon nephropathy

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To-day at least 60 case histories of glomerulonephritis associated with exposure to silicon have been published. Silicon is an element the salts of which, named silicates, are the main components in rocks and sand. Exposure to silicates is prevalent among miners, foundry and quarry workers, sandblasters, tile setters, glaziers, and workers in the production and handling of asbestos, mineral wool and fiber glass. The type of renal disease seen in such individuals is most often so-called focal, segmental glomerulonephritis, and a characteristic feature is the simultaneous presence of an auto-immune disease such as Wegener granulomatosis or systemic lupus erythematosus.

Case reports are weak evidence, because the association could occur by chance. However, there is also epidemiological evidence, that silicon or silicon salts may produce serious glomerulonephritis.

Cross-sectional studies of workers with occupational exposure to silicon compounds have shown that some of them may have urinary findings typical for early glomerulonephritis (Ng et al 1992, Ng et al 1993, Boujemaa et al 1994), even after a short exposure (Hotz et al 1995). After many years the exposure may result in serious kidney damage. In a cohort study of 2412 men who had worked on average eight years  in a South Dakota gold mine between 1940 and 1965 the incidence of end-stage renal failure in 1977 was significantly higher than in the general population; in particular end-stage renal failure due to glomerulonephritis (Calvert et al 1997). In a review of 583 reported cases of silicosis (a serious lung disease caused by chronic inhalation of silicates) in Michigan between 1985 and 1995 a reduction of renal function was found in about a third of them (Rosenman et al 2000).

Case control studies are also in support. In one such study of 272 patients with chronic renal failure and 272 people with normal renal function, 52 (19%) of the patients had been exposed to silicon-containing compounds but only 24 (8.8%) of  the control individuals. Among the various diagnostic groups 16% of 38 patients with glomerulonephritis, and 26% of 39 patients with diabetic nephropathy had been exposed (Nuyts et al 1995). In another case-control study fourteen of sixteen patients with glomerulonephritis and Wegener granulomatosis had been exposed to nephrotoxic chemicals, most of them to silica and silicon-containing compounds (Nuyts et al 1995).

As is the case with almost all other chemicals associated with glomerulonephritis, chemicals derived from silicon are known for having disturbing effects on the immune system, in particular it has been found that autoimmunity is a common finding, seen both in exposed workers, and in experimental animals (Tervaert et al 1998; Parks et al 1999)

Thus, although studies of silicon-associated glomerulonephritis are much fewer, these studies suggest that exposure to silicon may also lead to end-stage glomerulonephritis.

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