Strontium chromate

Carcinogenicity

Description of key information

There are no experimental studies of carcinogenicity of Sr-chromate by oral, dermal or inhalation exposure but there are numerous reports on carcinogenicity studies where strontium chromate and/or other hexavalent chromium compounds were given either by other routes which can be taken as substitutes of inhalation, i.e. by intratracheal or intrabronchial administration. 
Sr-chromate by intrapleural iplantation induced local tumours in 17/28 treated rats vs. 0/34 for the untreated rats. 
Among the chromium containing materials  which were studied for carcinogenic activity in a two year study using an intrabronchial pellet implantation, only three groups gave statistically significant numbers of bronchial carcinomas. Two of these were groups receiving different samples of strontium chromate had bronchial carcinomas in singnificantly increased amounts (43/99 and 62/99).
The epidemiological evidence on the inhalation carcinogenicity of poorly soluble hexavalent chromium is obvious as has been concluded in the carcinogenicity assessments of various international/governmental institutions.

Justification for classification or non-classification

Strontium chromate is a sparingly soluble experimental carcinogen. Slightly soluble or almost insoluble chromates have been carcinogens in animal tests and clear epidemiological evidence exists on their inhalation carcinogenicity.

The CLP classification of strontium chromate shall be Cat 1A.

Additional information

There are no experimental studies of carcinogenicity of Sr-chromate by oral, dermal or inhalation exposure. However, there are numerous reports on carcinogenicity studies where strontium chromate and/or other hexavalent chromium compounds were given by other routes which can be taken as substitutes of inhalation, i.e. by intratracheal or intrabronchial administration. Sr-chromate by intrapleural implantation induced local tumours in 17/28 treated rats vs. 0/34 for the untreated rats. Among the chromium containing materials which were studied for carcinogenic activity in a two year study using an intrabronchial pellet implantation, only three groups gave statistically significant numbers of bronchial carcinomas. Two of these were groups receiving different samples of strontium chromate had bronchial carcinomas in singnificantly increased amounts (43/99 and 62/99). The epidemiological evidence on the inhalation carcinogenicity of poorly soluble hexavalent chromium is obvious. Tumors have been produced in nearly every study utilizing the slightly soluble or insoluble particulates such as zinc, lead, strontium and sintered calcium chromate. A large number of published reports show that particulate chromates embody the highest risk because of adhesion to the cell surface followed by slow but chronic dissolution in the immediate microenvironment of the cell surface allowing released chromate oxyanions to escape extracellular reduction and be absorbed into the cell. Specific epidemiological studies where strontium chromate had been the sole or principal exposing agents do not exist. However, in some cohorts Sr-chromate exposures have been likely. Because the carcinogenic potential originates from the Cr(VI)-anions, this report reviews epidemiological studies where the exposing agents have been hexavalent chromium compounds. Exposures in various industries to hexavalent chromium have had association with elevated risks of respiratory system cancers. Some of these studies have even enabled dose-response analyses for quantitative cancer risk analysis.  A linear extrapolation (non-threshold) application of epidemiological studies suggests that there may be a 25% risk of lung cancer morbidity resulting from occupational exposure to Cr(VI)-containing dusts and mists under 52 microg/m3 Cr(VI), which was the exposure limit deemed permissible 1971 by the U.S. Occupational Safety and Health Administration (OSHA) in 1971. The U.S limit was readjusted in 2006 to 5 microg/m3, highlighting the fact that exposure to chromates continues to be a major public health issue.

Carcinogenicity: via inhalation route (target organ): respiratory: lung