Phytotoxicity of ancient gaswork soils. Effect of polycyclic aromatic hydrocarbons (PAHs) on plant germination

The phytotoxicity of various contaminated soils was assessed by plant inventories on ancient industrial fields and by phytotoxicity tests. Industrial fields are well colonised by numerous weedy plants. Phytotoxicity was tested with pure PAHs, ancient industrial soils, soil leaches, liquid tar and tar volatile compounds. Both field studies and toxicity tests show that contaminated samples can be classified into two categories: first, a recently excavated soil/liquid tar that was foul-smelling and phytotoxic and second, an ‘aged’, surface soil that was weathered and non-phytotoxic. Plant germination and growth are strongly inhibited by the presence of volatile, water-soluble low molecular-weight hydrocarbons (<3 rings) such as benzene, toluene, xylene (BTX), styrene, indene, naphthalene and other possibly toxic substances. On the other hand, high molecular weight PAH (3–5 rings) did not show any phytotoxicity under the conditions studied. These findings suggest that once low molecular weight aromatic hydrocarbons are removed, e.g. by volatilization, biodegradation, weathering, tillage and fertilising, plants should be able to grow.