On the origin of organolead compounds in wine
Résumé
The speciation pattern of organic lead has been determined in 22 samples of French wines from the Cotes du Rhone and the Rhone Valley regions, seven samples of Californian wines and two samples from Australia and Argentine. Methyllead species were ubiquitous in French wines (white, rose and red) while generally absent in American wine samples. A possibility of biomethylation of mineral lead has been examined by investigating the organolead speciation pattern at various stages of the alcoholic and malolactic fermentation both in natural grape must and in a synthetic matrix enriched in lead(II). No methylation of lead was observed while a slow degradation of triethyllead occurred as the fermentation was progressing. No formation of organolead compounds could be detected in lees and burbes where yeast and lactic bacteria can work under anaerobic conditions. This indication of the atmospheric origin of organolead in wine is further supported by much larger concentrations of organolead found in older vintages (even from the US and Australia) than in the present ones which is attributed to the decreasing use of leaded gasoline.