COMPARISON OF CHEMICAL-EXTRACTION AND BIOASSAY FOR MEASUREMENT OF METSULFURON IN SOIL

A new extraction method for the HPLC-UV determination of metsulfuron i n soil was developed and compared with NaHCO3 extraction and a lentil bioassay technique. The new procedure consisted of metsulfuron extract ion using anion exchange membranes followed by a dichloromethane conce ntration of the membrane eluates. Three soils representing different l andscape positions were spiked with metsulfuron to yield concentration s in the range of 0 to 40 mu g kg(-1) dry soil and were analyzed by th e above procedures. At a given spike rare, the efficiency of the anion exchange membrane extraction was highest for the soil from the upper slope position and lowest for the soil from the lower slope position, indicating that the amount of ion exchangeable sulfonylurea was affect ed by soil properties. Similar trends in degree of root growth inhibit ion were observed for lentil response to metsulfuron presence in soil; percent root: growth inhibition was related to the landscape position as the amount of membrane-extractable metsulfuron. The percent shoot growth inhibition was nor soil dependent and did not differ among soil s. The efficiency of NaHCO3 extraction for metsulfuron did not vary wi th soil type; in the NaHCO3 method, because of the buffered alkaline n ature of the extraction, differences in soil properties, particularly soil pH, would have less effect on metsulfuron recovery. Because of si milar trends for the results of the membrane extraction method and a l entil root bioassay, anion exchange membrane extraction may provide us eful information on bioavailable fractions of sulfonylurea herbicides in soil.