The Island of Chios (east Mediterranean), Citrus Plantations and the Mercury Nightmare

Abstract

Mercury poisoning, as a result of environmental pollution, has become a problem of current interest on a global scale. Natural emissions of mercury form two-thirds of the input; manmade releases form about one-third (Patra and Sarma 2000). Accumulation, toxicity response and mercury distribution seem to affect the plants and differ between plant species. It has been observed that the chlorophyll, protein and nitrogen, phosphorus, potassium contents decrease significantly with increasing Hg concentrations in young plants of Vallisneria spiralis (Gupta and Chandra 1998) while the lower the nutrient strength in the culture medium is, the higher the metal concentrations accumulated in the different plant parts (Gothberg et al. 2004). In plants of Bacopa monieri grown in high concentrations of Hg, the metal accumulation in the root tissues was about five times more than in the shoot (Sinha et al. 1996) while tobacco plants (Nicotiana tabaccum) are less tolerant to heavy metals, including Hg, than sunflower (Helianthus annuus) (Ruso et al. 2001). Salix species investigated for heavy metal uptake were found to absorb Cd and Zn at a rate higher than they absorb Ni, Hg, Cu and Pb (Labrecque et al. 1995). Chios is a Greek island globally known for the mastic trees (Pistacia lentiscus var. chia) and their products. It is located at the north eastern part of the Aegean Sea, just three and a half miles from the coast of Asia minor. The bed of the main water basin extending below the farmlands of the island, is composed of cinnabar (a mineral containing Hg). During the summer months, excessive pumping for plant irrigation lowers the underground water level by 12–15 cm daily! In a few weeks water starts to turn salty since seawater intrudes the basin. This change induces the release of mercury in the water through the reaction of NaCl with the cinnabar substrate. It is common that mercury concentration, in the basin’s water, raises to 7.5 lg Hg/L while the upper limit posed by the European Union directive is 1 lg Hg/L. It seems that the local authorities and the islanders have to deal with a serious problem. Given the water shortage in most Mediterranean islands and the extensive cultures of citrus fruits established on Chios island, a serious approach to the mercury problem has to be made. Although there is a tendency for mercury to accumulate in roots, indicating that roots serve as a barrier to mercury uptake (Patra and Sarma 2000), only after a thorough investigation can leaves and, mainly, the fruits of citrus trees be considered free of mercury contamination.