It is well known that certain pollutants or classes of pollutants have detrimental effects on the environment, such as ozone (triatomic oxygen) depletion and global warming, and on our health when pollutants are beyond “acceptable” levels. Vineyards are typically located in areas with low pollution levels and are therefore not a major concern. This does not mean that pollution should be ignored; however, limited research has been done on the impact of pollution on vineyards. This is a very complex area of research. Let’s examine the chemistry of pollutants and especially their effects on vine cultivation.
Earth’s atmosphere is made up of a number of gases, primarily diatomic nitrogen and oxygen, as well as carbon dioxide and water vapour. And every second of every day, pollutants from car emissions, landfills and industrial processes are released into the atmosphere and react with its components. The main pollutants are sulfur oxides, carbon dioxide, nitrogen oxides, chlorofluorocarbons (CFCs), and when they reach the atmosphere, they react with sunlight and atmospheric (diatomic) oxygen to form harmful substances.
Sulfur dioxide is known to have harmful effects on plants at high concentrations; It is the result of oxidation of elemental sulfur, as in coal combustion processes. It also reacts with atmospheric oxygen to form sulfur trioxide, which then reacts with water vapor to form sulfuric acid in acid rain. A second component of acid rain is carbonic acid, which is formed by a similar reaction from emitted carbon dioxide. And the most harmful component is hydrofluoric acid, which consists of hydrogen fluoride from smelting operations and phosphorus fertilizer production, and water vapor in the atmosphere. When acid rain reaches the soil in vineyards, it lowers the pH, thereby disrupting the soil chemistry and making it difficult to grow premium grapes. Some of these acids are particularly corrosive and toxic and harmful to vine cultivation.
Nitrous oxide is found in car exhaust gas and is the result of high-temperature combustion of (diatomic) nitrogen. In the atmosphere, nitrogen oxide reacts with molecular oxygen to form nitrogen dioxide, the reddish-brown gas responsible for smoke. Nitrogen dioxide is then photochemically converted back to nitrogen oxide together with an oxygen atom. The oxygen radical then reacts with molecular oxygen to form ozone in the lower atmosphere. Ozone is a strong irritant and damages vines and crops.
Car exhaust also releases hydrocarbons that react with nitrogen oxide to form peroxyacetyl nitrate, a compound belonging to the class of peroxyacyl nitrates, or PANs, powerful toxic irritants that cause ozone to accumulate in photochemical smoke. PANs cause high damage to grapevine physiology, resulting in reduced yield. And until leaded (tetraethyl lead) gasoline was phased out, wines produced from vineyards located near high-traffic roads showed higher levels of lead, a potent neurotoxin responsible for lead poisoning. If lead enters the bloodstream, it can interfere with and disable the delta-aminolevulinic acid dehydratase (ALAD) enzymes responsible for making hemoglobin. Hemoglobin is an iron-containing protein pigment that occurs in the red blood cells of vertebrates and functions mainly in the transport of oxygen from the lungs to the body tissues. Lead poisoning can then cause irreversible neurological damage, along with abdominal pain, gastrointestinal problems, headaches, anemia, reproductive problems, and numerous other effects.
Chlorofluorocarbons (CFCs) belong to the class of haloalkanes, meaning they include alkanes such as methane or ethane and halogens such as chlorine or fluorine and are well known to have detrimental effects associated with ozone depletion. The halogen in CFCs reacts with ozone to form an oxide of halogen plus molecular oxygen.
As for pesticides, it has been clearly proven that negligible residues are present in wine, despite environmental influences. Of course, this assumes pesticides are applied appropriately and within the recommended treatment period before harvest. And various winemaking processes, namely crushing, pressing, fermentation, refining, straining and aging all result in the destruction of pesticide residues.
But what about the thick, dense smoke from the devastating wildfires that swept through Northern California wine country in the summer of 2008? Some red wines from hard-hit areas like Mendocino County have decidedly smoky, charred aromas and a burnt wood, ashy flavor. The compounds responsible for smoke spot, guaiacol and 4-methylguaiacol, are volatile phenols, which are absorbed into grape skins – particularly in thin-skinned varieties like Pinot Noir – and then extracted during maceration and aggravated by fermentation. Since there is no skin maceration by the juice, the whites are mainly preserved. Many studies have been conducted on smoky wines in Australia in 2003, where smoke from forest fires also affected vineyards to a great extent.
Using reverse osmosis and nanofiltration technologies, the Australians were able to reduce the culprit compounds to undetectable levels. VA Filtration (VAF)By treating the affected wine, a company specializing in services such as the removal of volatile acidity (VA), Brett (yeast infection), and TCA (wine with pistachios) claims they can now eliminate ninety-nine percent of their targeted sensory properties. With food grade resin developed in Germany. Interestingly, though not surprisingly, the VAF website states that “the offensive compound(s) being removed is still [known]”
But the astute reader will also know that guaiacol and 4-methylguaiacol are compounds found in highly desirable, roasted oak aged wines. This is a complete dilemma!