Persistent herbicides (PH) pose an existential threat to commercial, municipal and community composting, and to the emerging circular economy. PH have been found in composts in many states and have cost compost producers millions of dollars. A survey of US Compost Council members composts revealed that approximately 4% of ready to sell composts have phytotoxic levels of PH. Common garden plants including tomato and bean are sensitive to these compounds at concentrations below 10 ppb. Chemical analysis is inconsistent and requires expensive liquid chromatography and mass spectrometry equipment, as well as highly trained analytical chemists, to detect in composts at these concentrations. A number of bioassays have been developed for the detection of these compounds. Methods differ in plant species used, watering methods, mix rations, and rating systems. In my work I applied some of these past methods to create an easy to use and follow approach that anyone could do. I started with the general peat moss and compost ratios and worked up to an approach that does not use potted plants at all, but soil blocks in planting trays. A clay based soilless media was tried but proved to be ineffective and temperamental and thus disqualified for further investigation. Soil blocks proved to be effective as many plant species and samples could be analyzed in series with minimal equipment and experimental footprint in a green house or under grow lights indoors. I found that most methods used large quantities of material, while not all that much is required to get representative samples. The best bioassay is the one that is used and detect PH at phytotoxic levels, and this approach is a fair and measured approach that can be used by compost producers to screen their ready to sell compost for potential PH contamination.
Speakers: Gerard Braun
Duration: 19 minutes
Credits: 0.5
Member Price: $30.00
Non-Member Price: $52.50
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PRO.215-Development of Detailed Bioassays for Persistent Herbicides-AC22.CREF
