Variability of bioassays with metsulfuron-methyl in soil

A total of 74 independently run bioassays with soil incorporated metsulfuron-methyl from 12 different laboratories was analysed by a logistic dose-response curve to assess the precision of regression parameters and relate ED(50) to soil properties. The potency in terms of ED(50) of metsulfuron-methyl in Brassica rapa L., which was used by all laboratories, varied between 0.05 and 3.9 g a.i. ha(-1). ED(5)0 was negatively correlated with pH and positively correlated with organic matter. The majority of laboratories had EDso within the interval 0.1-1.0 g a.i. ha(-1). At one laboratory using three test species, the most sensitive species was Beta vulgar's L. followed by Brassica rapa L, and Lepidium sativum L. The coefficients of variation were smallest for the ED(50) and ED(90) response levels and largest for the ED(10). The slope of the response curves had considerably lower coefficients of variation than the EDs. The results are discussed in relation to a previous collaborative bioassay study. Finally it is suggested that standardization of bioassays with herbicides could be achieved in the same way as standardization of chemical analyses.