Radiometric studies of mercury loss from fungicidal paints. 1. Loss of phenyl mercuric acetate

Abstract

Exposure tests have been made on paint films prepared from an emulsion paint containing phenyl mercuric acetate (PMA) labelled with 203Hg. Loss of mercury from the films has been followed radiometrically. Films exposed indoors in a confined space (no air circulation) showed little, if any, mercury loss for up to 8 months. Films exposed in the open laboratory lost from 20 to more than 60% of mercury after 250 days. This agrees qualitatively with the results of other workers on similar paints. At 50°, films lost mercury at rates about 10 times greater than those at ambient temperature. Films exposed out‐of‐doors lost the majority of their mercury after a few days of rain. Pre‐treatment of films, e.g. by u.v. radiation, had no effect on their subsequent outdoor behaviour. Even well‐dried films lost mercury at the same rate as newly applied films. Films with a low PMA content (0·02% Hg) lost mercury at a higher percentage rate than films with a high one (0·2% Hg). Thick films (0·002 in.) lost mercury at a lower rate than thin ones (0·001 in.). A mercury‐free top coat also reduced loss rate. All loss rates decreased with increasing time. These trends applied to all the exposure conditions studied. Mercury loss appears to be due to both volatilisation and dissolution of PMA and not to decomposition. The results indicate a non‐homogeneous distribution of PMA throughout the paint film, and a diffusion‐controlled process.