Degradation of [14C]ethylenethiourea in surface and subsurface soil

Degradation of 0.07 mg/kg 14C-labelled ethylenethiourea (ETU) was determined in surface and subsurface in coarse sandy field soil from Denmark. Surface soil from 15 cm depth was sieved and incubated in Erlenmeyer flasks at 21°C. Subsurface soil from 60 and 100 cm depth was incubated as undisturbed soil cores in steel tubes at 10°C. The effect of incubation in undisturbed or mixed samples were determined. The mineralization of ETU in surface soil was rapid: 19.5 ± 4% of added 14C was evolved as 14CO2 after 24 h of incubation. In subsurface soil an overall lower rate of mineralization of ETU was found, and at 100 cm depth mineralization was slower than at 60 cm; 16.3 ± 4.1% and 23.5 ± 3.8% of added 14C being evolved as 14CO2 after 109 days of incubation, respectively. Exponentially increasing evolution of 14CO2 indicating proliferation of decomposers was seen in most samples from both surface and subsurface soil samples. The slow degradation of ETU in subsurface soil compared with surface soil implies a greater risk of groundwater contamination once ETU has leached to the subsurface.