Biological monitoring and accumulation of airborne mercury in vegetables

Abstract Grass cultures can be used for the biological monitoring of mercury pollution in ambient air, because the measured mercury accumulation in grass cultures gives a reliable indication of the average concentrations found in leafy vegetables. However, for washed leafy vegetables, the concentrations are usually lower than those found in grass. The mercury accumulation found in herbs, especially in perennials, is far higher than that in grasses and leafy vegetables. There is apparently a long-term accumulation similar to the pattern found in oak leaves at the end of the growing season. Nevertheless, there exists a clear relationship between the concentrations found in herbs and those in grass cultures. No such relationship could be detected for roots, tubers, bulbs, fruits or leguminous vegetables. The fairly low concentrations found in roots, tubers and bulbs (ten times less accumulation than grass in containers) and in fruits and leguminous vegetables (factor 25 less) apparently result from an accumulation from the soil and less from a direct deposition of airborne mercury. The simple technique of permanent grass cultures sampled every 28 days is very useful for a general survey of atmospheric pollution. Shorter integration periods are necessary to monitor the fluctuations in mercury pollution and alternating grass cultures (14-day exposure) are preferred. There exists a clear relationship between these two biomonitoring techniques.