Lead contamination in Portuguese red wines from the Douro region: from the vineyard to the final product

To quantify lead contamination in wines and to try to identify major lead sources, two winemaking processes were followed during one annual cycle of wine production. Two vineyards from the Douro Portuguese region and two types of wine, one red table wine, which has been produced in a very modern winery, and one red fortified wine (similar to Port), which has been produced by a traditional vinification process, were selected for this study. Aerosols from the vineyards atmosphere, vineyard soil, vine leaves, grapes, and samples from the intermediary and final wine product were collected. Suitable pretreatments, namely, high-pressure microwave assisted digestion (soil, leaves, and grapes) and UV-irradiation (grape juices and samples from the different steps of the vinification processes), were used. The samples were analyzed in terms of lead total concentration and respective isotope ratios by using inductively coupled plasma mass spectrometry and atomic absorption spectrophotometry with electrothermal atomization. It was observed that the major sources of lead were in the vinification system, the more traditional one introducing more lead than the modern one. For the fortified wine, the lead concentration increased from 4.7 mug L-1, in the grape juice, to 17.2 mug L-1, in the final product, while for the table wine the increase was from 4.1 to 13.1 mug L-1. Therefore, only about 1/4 (fortified wine) and 1/3 (table wine) of the lead total content of the final products came from soil and atmospheric deposition. Therefore, it is expected that marked reductions of the lead content in the wines would occur if the sources of lead were removed from the tubes and containers used in the vinification system, particularly by using welding alloys and small fittings free of lead. The lead levels in the vine leaves (global mean of 0.43 mug g(dry leave)(-1)) and grapes (global mean of 35 ng g(dry) (-1)(grape)) were similar in both vineyards.