A numerical method for selecting low toxicity
plasticizers for
glycol methacrylate (GMA) embedding mixtures is described. It involves use of various numerical parameters, namely; molecular weight, melting point, solubility parameter, and toxicity data. On the basis of these parameters, nine
plasticizers were selected. Their effects on microtomy and tissue processing, and also their influence on tissue morphology and staining, were investigated. For tissue processed at low temperatures into GMA, using
ethanol dehydration, the following compounds were as satisfactory as
2-butoxyethanol whilst being less toxic: 2-isopropoxyethanol,
2-(2-methoxyethoxy)ethanol,
2-(2-ethoxyethoxy)ethanol, 2-(n-butoxyethoxy)ethanol. However for tissues processed using the
plasticizer as dehydrating agent, the optimum
plasticizers were 2-isopropoxyethanol,
2-(2-methoxyethoxy)ethanol and
2-(2-ethoxyethoxy)ethanol. It is possible to give a numerical specification of the preferred
plasticizers, and for the first procedure this is: a solubility parameter in the range 21-26 J0.5 cm-1.5 or higher, a melting point well below 0 degree C, and a rat oral LD50 greater than 12.52 mmol kg-1. It was also possible to analyse the differential effects of the dehydrating agents on histochemical and
enzyme histochemical staining on a numerical basis, using a structure-activity relations approach.