DRY ASH, A BETTER REFERENCE BASE THAN DRY-MATTER FOR HEAVY-METALS AND OTHER PERSISTENT POLLUTANTS

Concentrations of pollutants in biotic materials are usually related to dry matter. This work demonstrates with the use of heavy metal-contaminated poplar leaves (Populus nigra 'Italica'), that ash of dry matter (dry ash) obviously yields a better reference, as it eliminates the natural variations among organic substance contents. Values of heavy-metal concentrations in dry ash of leaves were generally more homogeneous and better correlated with corresponding values in air and soil than those in dry matter. It is further shown that concentrations of non-biodecomposable and non-volatile pollutants in the mineral fraction (the same as ash) of, for instance, plants and their residues (autumn leaves, mulch compost) can directly be compared with those in soil (nearly 100% mineral), and vice versa. This facilitates the setting of maximally permissible values for pollutant concentrations in plant dry matter or their residues, and in soil, which can be used in the protection of soils against pollutants accumulated in fresh or fallen leaves, mulch or compost. In this connection, the heavy-metal and lindane margins in West German regulations for issuing environmental certificates for compost products are discussed. © 1990 Kluwer Academic Publishers.