Volatility of fungicidal mercury compounds on wheat seeds

The volatility of two fungicidal seed dressings, Panogen 15 B liquid and Panogen PX powder, containing methyl mercuric dicyandiamide in equivalent amounts at the dosage used, was compared with that of triple distilled mercury. Tests were made in the absence and presence of cleaned Manitou wheat of 12.0% and 17.1% moisture content. The Panogen formulations were compared at the recommended and twice the recommended rate at different dosages, storage periods and storage temperatures. The Hg content of air samples was determined by the Corte-Monkman method, capable of determining 0.4 ng of Hg, which in a 1-L air sample is equivalent to 0.049 ppb (v/v). The volatility of the interstitial air expressed as mug of Hg vapor/m3 air depended on temperature, wheat moisture content and storage duration and ranged from 150 to 2,240 for metallic Hg, 21 to 350 for Panogen 15 B, and 31 to 380 for PX. In the absence of wheat the volatility of 15 B was greatest (395) at -17.5 degees C and least (75) at 4.5 degrees C, but increased rapidly thereafter with increased temperature. Volatility of metallic Hg after application to wheat of 12.0% and 17.1% moisture content was not significantly reduced after four days storage, but that of Panogen 15 B and PX was reduced considerably, particularly at the higher moisture level. Thus, volatility of mercurial seed dressings cannot be predicted from Hg content alone. Reduction of volatility through possible irreversible chemical bonding of Hg with seed components is suggested for more detailed investigation.