Transformation of [14C] and [35S]labeled lignosulfonates during soil incubation

¹⁴C] and ³⁵S]labeled lignosulfonates (LS) or ¹⁴C]labeled coniferyl alcohol dehydropolymer (DHP) were aerobically incubated in soil for 17 weeks. Respiratory ¹⁴CO₂ was compared with that from DHP or that from U¹⁴C]cellulose. Less CO₂ was released from ring and side chain carbons of LS than from DHP, though similar amounts of CO₂ were released from the methoxyl groups of both compounds. After incubation, the soil samples were exhaustively extracted with water and then with a sodium pyrophosphate-NaOH solution. The water solubility of the originally completely-soluble LS carbons was greatly decreased by incubation, and a large portion of the extracted ³⁵S was detected as sulfate. The pyrophosphate extract was separated into humic and fulvie acids. The humic acid from soils incubated with LS contained low ³⁵S activity and a similar ¹⁴C activity to that from soils incubated with DHP. The fulvic acid from the soils incubated with LS contained higher amounts of ¹⁴C (and ³⁵S) than that of the soils incubated with DHP. More side chain ¹⁴C activity than other ¹⁴C activity was found in both, the water extract and the fulvic acid from soils incubated with LS. The high ³⁵S together with the high side chain ¹⁴C activity probably indicates an elimination of the side chain carbons together with sulfonic acid groups. Anaerobic incubation of soil with LS or DHP promoted breakdown and incorporation of LS and DHP into humus much less than aerobic incubation. The possible reduction in potential pollution from lignosulfonates due to the observed transformations in soil are discussed.