METHODS TO MONITOR MITC FOR PHYTOTOXICITY AND IN THE ENVIRONMENT

Soil fumigation with the methyl isothiocyanate (MITC) generators metam-sodium, metam-potassium and dazomet gives rise to residual gasses that need to be checked prior to sowing or planting. Different factors determine the residual amount: dose rate, soil type, soil organic matter content, soil humidity, soil temperature, soil porosity and tarping. Under practical conditions this safety check is made after soil tarp removal or, if not covered by plastic film, prior or after soil aeration e.g. by rotovation. Forced aeration is often standard practice and will speed up the removal of potential phytotoxic gasses. MITC monitoring will help to decide on the necessity of forced aeration or even repetition of it. Classic test for phytotoxic risk evaluation only is the cress seed germination test. Alternative seeds, such as lettuce, are also in use. This is the slowest method, needing at least 2 days. Another possibility of monitoring is the use of specific gas detection tubes giving sensitive response within 3 minutes and especially of interest in the fumigated environment, e.g. operator and bystander exposure or risk for neighbouring residents. A hand held pump is needed and the tubes are consumables. A specific measuring principle is by quartz micro balance (QMB). This is also known as the ‘electronic nose’ and was beyond other applications also developed for MITC. The instrument can become operated in the field with a car power adaptor. The whole procedure takes 45 min. Photo ionization detection is possible with hand held instruments. It is not very specific but among MITC and other volatile and active degradation compounds majority of the instrument response is for MITC with a 10.6 eV lamp. It is also very useful for environmental monitoring. Measuring and response time is a few seconds. Other possibilities need to become explored or are under consideration, e.g. infrared analyzer allowing specific detection.