Toxicological assessment of heat transfer fluids proposed for use in solar energy applications, II

Abstract

Ten commercially available solar heat transfer fluids as well as three samples of used fluids (an ethylene glycol, a propylene glycol, and a silicone fluid) obtained from operating solar hot water systems were evaluated for acute oral toxicity in female rats and for dermal and ocular irritation in female rabbits. Mutagenicity testing was conducted in the Salmonella mutagenicity assay (TA 1538, TA 98, TA 1535, TA 100). Oral LD 50 values ranged from 7.0 g/kg for ethylene glycol-based products to >24 g/kg for propylene glycol, hydrocarbon oils, and silicone fluids. None of the solar fluids was mutagenic at the concentrations tested nor caused more than a slight ocular or dermal irritation. No appreciable differences were observed in evaluations between used and unused fluid samples. The results indicate that the fluids may be considered relatively safe for residential solar energy applications, although based on toxicity testing propylene glycol should be preferred over ethylene glycol. Trifluoroethanol (Fluorinol 100) was included in these studies because of its probable use as a working fluid in organic Rankine cycle waste heat recovery systems. Trifluoroethanol had an LD 50 of 0.21 g/kg, was not irritating to rabbit skin nor mutagenic in Salmonella, but demonstrated severe ocular toxicity.