Heavy metals may become a public health issue that affects foodstuffs as well as alcoholic beverages.
Dr Dee Blackhurst & Prof Dave Marais, UCT Faculty of Health Sciences
It is accepted that moderate consumption of alcoholic beverages, particularly wine, and more especially red wine, has certain health benefits, as reviewed by Blackhurst. It therefore caused some concern when it was found that wine from certain European countries such as Slovakia and Hungary, contained high concentrations of heavy metals . The same authors found a variety of metal ions at relatively high concentrations in red wine, compared with stout and apple juice. Several potentially toxic metal ions that were not found in the stout and apple juice (for example vanadium, nickel and cadmium), were found in the red wine, although all three beverages contained many other metals such as chromium and lead . The authors expressed concern over the potentially toxic effects for those who consume at least 250 mL red wine daily over a long period of exposure.
Heavy metals may thus become a public health issue that affects foodstuffs as well as alcoholic beverages. Before public health recommendations can be made about the inclusion of wine in lifestyles, there needs to be clear evidence that the benefits of wine consumption outweigh any possible health disadvantages. Informed decisions by consumers can only be made by declaring the possible harmful constituents in wine and foodstuffs, as well as daily limits.
The definition of ‘heavy metals’ is sometimes inconsistent, but refers to a group of metals associated with ecotoxicity. In a broad sense, those metal ions that can be considered ‘heavy metals’ are: arsenic, cadmium, chromium, copper, iron, lead, manganese, mercury, molybdenum, nickel, strontium, vanadium, and zinc. Heavy metals may loosely be assigned to four functional classes: class A metals are essential for life in relatively high amounts (for example iron), class B includes metals that have no known biological function but are not particularly toxic at low concentrations (for example strontium), class C includes metals that are essential in very low concentrations (copper, molybdenum, nickel, manganese, and zinc), but which at higher than certain threshold concentrations may become toxic, and finally class D, which includes metals that are toxic even at low levels and their biological function is unclear (cadmium, mercury, and lead) .
In humans, several of the heavy metals are important trace elements obtained in the diet. They can generate reactive oxygen and nitrogen species, which may have beneficial effects. The beneficial effects include the defence against infection, normal dilatation of blood vessels and signalling inside cells. They may also neutralise certain free radicals when they are part of enzymes such as superoxide dismutase (copper, zinc, and manganese). Furthermore, cellular respiration requires iron whilst maintenance of cell membranes also requires some heavy metals. In these ways heavy metals may protect against ageing and certain cancers .
Heavy metals may originate from a number of different sources, both natural and anthropogenic. Through agricultural use of heavy metals (pesticides, fungicides and fertilisers), mining, coal and oil combustion, stormwater runoff may discharge heavy metals into oceans. Crops may become contaminated, and thus foods and beverages may become a significant source of these metals. It has been established that of the heavy metals, arsenic, cadmium, chromium, mercury, and lead are particularly ecotoxic and detrimental to human health .
Mercury is a very toxic heavy metal, and because its vapour can be inhaled or it can be transported as a salt or organic compound in water and fat, it is considered a global pollutant. Every year anthropogenic sources produce approximately 2 500 tonnes of mercury, and efforts are being made to secure a global network whose aim is to monitor mercury pollution . Several countries, including South Africa, have expressed interest in this.
The use of lead by man dates back to at least 3500 B.C. Human skeletons dating to prehistoric times contain less than one percent of lead recorded during present times . The Romans used lead extensively: in their plumbing, their aqueducts, and in many of their cooking utensils. Lead was also used in wine-making, to preserve and even to improve the taste of the wine. The large scale use of lead caused health problems amongst the Romans. The sequelae included severe abdominal pain, and paralysis. Gout was also associated with the chronic lead poisoning . Adults absorb less lead from the diet than infants (5 – 15% compared with 30 – 40%), raising the concern for childhood nutrition. Excessive lead exposure is associated with carcinogenesis, birth defects and hypertension . Until the 1990s, lead concentrations in wine were often greater than 150 g/L, but these are gradually decreasing owing to measures taken to reduce total lead emissions, and also the replacement of old equipment in the wine-making process .
Arsenic and chromium bind to proteins, altering their structure and function, thereby promoting cancer. An excess of copper, molybdenum, and zinc may be associated with vague manifestations such as fever, nausea, vomiting, diarrhoea, and anaemia , but harm may already occur at lesser exposure. Intake of several heavy metals has been associated with different neurodegenerative diseases, for example employees in the heavy metal industry exposed for more than twenty years to metals such as copper, manganese, and lead, were found to suffer more frequently from Parkinson’s disease . A recent study found an approximate doubling in the risk of Parkinson’s disease in people who supplemented their diet with iron and manganese . Lead and cadmium were found to inhibit memory and learning .
In certain regions affected by contamination of local food produce by heavy metals, populations can be at high risk if their food consumption is not diluted by food from non-contaminated areas .
Wine is a complex solution of water, alcohols, phenolic compounds, organic acids and residual sugars. Wine also contains varying concentrations of metal ions such as sodium, potassium, calcium, magnesium, nickel, chromium, zinc, manganese, cobalt, copper, iron, and lead . White wine generally has lower concentrations of these metals (except possibly cadmium and lead) than red wines, due mostly to the white wine-making process which uses fermentation without skins, and grape skins contain higher concentrations of metal than pulp . The metals in wine also vary at different stages of the wine-making process. During fermentation, metal concentrations decrease due to precipitation. Yeasts also consume metals such as copper, iron, and zinc . Clarification of wine may also lead to a decrease in concentration of heavy metals. Increases in heavy metals in wine may result from long maceration times, and long contact times with metal-containing equipment.
South Africa has set limits for some heavy metals in wine (Table 1). The European Union has no laws stipulating upper limits of concentrations of undesired substances in wine, though guidance is given by the OIV (Organisation Internationale de la Vigne et du Vin).
The source of heavy metals in wine could be the grapes, the processing of the grapes to wine, bottling, and storage. The variety and age of the grapes also play a role in the heavy metal content of wines. Grapes may become contaminated with heavy metals through the soil in which the vines are grown. This is a major source of heavy metals in wine, originating from, for example, weathering of rocks, or from environmental pollution. Wine is also in contact with various metals such as aluminium, steel (chromium, iron, manganese, and nickel) and brass (copper, zinc, lead, and nickel) during the wine-making process. Various metals contribute to particular characteristics in wine such as colour, flavour and aroma. The fermentation process is influenced by copper, iron, manganese, and zinc . With the exception of zinc, these metals are also part of an important antioxidant process that prevents spoilage in wine . There is little doubt that concerted efforts to minimise practices that may contribute to exposure of heavy metals, such as the use of mercury in dental amalgam, result in a decreased intake of these metals. A study in Sweden found annual decreases in lead and mercury between 1990 and 1999 of approximately five percent. The higher concentrations of heavy metals in wines from some countries may shift the consumption to wine emanating from countries which record lower values.
Moderate wine consumption may thus provide essential metals that contribute to health. As long as the wine consumption does not result in excessive exposure to these or other heavy metals, the regular consumption may not only promote health but also reduce cardiovascular disease. In order that this is the case, limits have been set for the heavy metal contents of wine (Table 1). Although the costs would have to be taken into account, the testing and labelling of South African wines for their heavy metal content could improve the consumption of our wines internationally.
For more information contact Dee Blackhurst at tel (021) 406-6108, e-mail email@example.com.