Mercury in Plants from Fields Surrounding a Contaminated Channel of Ria de Aveiro, Portugal

Samples of plants and soil were collected in March and June 1995 at 12 sites in fields surrounding the Estarreja Channel (Ria de Aveiro), where the mercury-rich effluent of a chlor-alkali plant has been discharged since the 1950s. Mercury concentrations in soil ranged from 0.64 to 182 μ g g−1. The highest values were attributed to soil contaminated with sediments dredged from the Estarreja Channel. Plant roots contained between 0.03 and 3.2 μ g g−1 of total mercury, and there is evidence that root systems uptake mercury from the soil. The linear relationship between mercury concentrations in the roots of Holcus lanatus and in soil over a wide range of mercury concentrations suggests that mercury uptake depends on the element's concentration in the soil. The ratio root:soil concentrations for the analyzed plants varied between 0.003 and 0.199, indicating varying mercury uptake by the root systems. Levels of mercury in the aerial parts of plants showed no clear relationship with the values found in soil or in roots, presumably being influenced mostly by the atmospheric deposition of airborne particles or absorption of atmospheric mercury.