How reliable are crystalline silica dust concentration measurements?

To determine how reliably commercial laboratories measure crystalline silica concentrations corresponding to OSHA's proposed limits, 105 filters were prepared with known masses of 20, 40, and 80 µg of respirable quartz corresponding to airborne silica concentrations of 25, 50, and 100 µg/m(3) and were submitted, in a blind test, to qualified commercial laboratories over a nine month period. Under these test conditions, the reported results indicated a lack of accuracy and precision needed to reliably inform regulatory compliance decisions. This was true even for filters containing only silica, without an interfering matrix. For 36 filters loaded with 20 or more micrograms of silica, the laboratories reported non-detected levels of silica. Inter-laboratory variability in this performance test program was so high that the reported results could not be used to reliably discriminate among filters prepared to reflect 8-h exposures to respirable quartz concentrations of 25, 50 and 100 µg/m(3). Moreover, even in intra-laboratory performance, there was so much variability in the reported results that 2-fold variations in exposure concentrations could not be reliably distinguished. Part of the variability and underreporting may result from the sample preparation process. The results of this study suggest that current laboratory methods and practices cannot necessarily be depended on, with high confidence, to support proposed regulatory standards with reliable data.

Developmental toxicity study of pentachlorophenol in the rabbit.

The potential for developmental toxicity of pentachlorophenol (penta) was studied in New Zealand white rabbits at doses of 0 (corn oil), 7.5, 15, and 30 mg/kg/day administered by gavage on days 6 to 18 of gestation. The rabbits were sacrificed on day 29 of presumed gestation and necropsied. Measurements included number of corpora lutea, pregnancy, number and distribution of implantations, early and late resorptions, live and dead fetuses, fetal weight, gender, and gross external, soft tissue, and skeletal alterations. The mid and high doses reduced maternal body weight gain; the high dose caused transient weight loss and reduced feed consumption. There were no effects on embryofetal development at any of the doses evaluated. Based on these data, the maternal no-observable-adverse-effect level (NOAEL) is 7.5 mg/kg/day, while the developmental NOAEL is 30 mg/kg/day. Penta is not a developmental toxicant in a nonrodent animal model.