Inter-Laboratory Validation Of An ISO Test Method For Measuring Enzyme Activities In Soil Samples Using Colorimetric Substrates

Abstract

Abstract The evaluation of soil quality requires the use of robust methods to assess biologically based-indicators. Among them, enzyme activities are used for several decades, but there is a clear need to update their measurement methods for routine use, in combining feasibility, accuracy and reliability. To this end, the platform Biochem-Env optimised a miniaturised method to measure enzyme activities in soils using colorimetric substrates in micro-well plates. The standardization of the method was carried out within the framework of ISO/TC 190/SC 4/WG 4 "Soil quality – Biological methods” workgroup, recommending an inter-laboratory evaluation for the publication of a full ISO standard.That evaluation, managed by the platform, was based on the measurement, in six soils of contrasted physicochemical properties, of the ten soil enzyme activities described in the standard. Eight laboratories were involved in the validation study. Only 2.7% of outliers were identified from the analyses of the whole dataset. The repeatability and reproducibility of the method were determined by computing, respectively, the intra-laboratory (CVr,) and inter-laboratory (CVR) coefficients of variation for each soil and enzyme. The mean CVr ranged from 4.5% (Phosphatase) to 9.9% (αGlucosidase), illustrating a reduced variability of enzyme activities within laboratories. The mean CVR ranged from 13.8% (Alkaline Phosphatase) to 30.9% (Phosphatase).Nevertheless, the method was repeatable, reproducible and sensitive. It also proved to be applicable for measuring enzyme activities in different types of soils. These results have been found successful by ISO/TC 190/SC4 and resulted in the publication of ISO 20130:2018 standard.