Phytotoxicity data safeguard the performance of the recipient plants in leachate irrigation

Leachates from an operating and a closed landfill were examined for their phytotoxicity by seed germination/root elongation tests using seeds of Brassica chinensis and Lolium perenne. Their EC50s ranged from 3% to 46% v/v, which varied remarkably with the operating status of the landfills. Seedlings of twelve tree species were grown in pots, which were irrigated with landfill leachate at the EC50 levels, with tap water as control. No tree mortality or growth inhibition was observed after 90 days of leachate application. Chlorophyll fluorescence measurement also showed that plants receiving leachate did not suffer from a decline in photosynthetic efficiency. Litsea glutinosa and Hibiscus tiliaceus had remarkable growth, and other non-N-fixers were not inferior to the N-fixing Acacia auriculiformis. Leachate irrigation improved soil N content, though P deficiency is still a problem. The seed bioassay provided a conservative estimate of the phytotoxicity of landfill leachate. Plants irrigated can be protected from growth inhibition when the leachate irrigation plan is designed with reference to phytotoxicity data.