Miniaturized test system for soil respiration induced by volatile pollutants

A miniaturized method based on 96-well microtitre plates was developed and used to study respiration in pristine and contaminated soils following addition of volatile substrates. Small soil samples were exposed to fuel components, which were volatilized from spatially separate reservoirs of 2,2,4,4,6,8,8-heptamethylnonane (HMN) as an organic carrier. Respiration was determined as CO2 production by means of a pH-indicator and bicarbonate-containing agar, or as 14CO2 evolution from 14C-labelled substrates. Substrate concentrations inducing maximum microbial activity or inhibition were determined and CO2 production profiles examined by multivariate analysis. When high concentrations of fuel components were applied, distinction of hydrocarbon exposed soils from unexposed soil was achieved within 6 h of incubation. With low concentrations, adequate distinction was achieved after 24 h, probably as a result of community adaptation. Nutrient limitation was identified with the 14C method for toluene, and the optimal N and P amendment determined. Further potential applications of this rapid and inexpensive method are outlined.