Biological and chemical degradation of tetraethyl lead in soil

Abstract

Tetraethyl lead (TEL) was first introduced by General Motors as an antiknock agent in gasoline in 1923. Its analogous chemical tetramethyl lead (TML) was introduced in 1960. The two chemicals were added to gasoline either singly or as mixtures to achieve desired octane numbers. Higher levels of lead in the urban environment have been attributed to extensive use of leaded gasoline in automobiles for over 50 yrs. With the advent of more sensitive analytical techniques in the late 1970 and early 1980, alkyl lead compounds were detected in aerosol dusts, rainwater, surface water, snow, sediments, soils, fish, and leaves. Ionic trialkyl lead (Triethyl lead (TREL) and trimethyl lead (TRML)) were the major species found. With the discontinuation of the use of leaded gasoline in automobiles the levels of alkyl lead in the environment should decline. Degradation pathways of tetraalkyl lead compounds in soil are not known. However, degradation pathways for tetraalkyl lead in aqueous solutions were proposed to proceed through a series of sequential dealkylation, and eventually to inorganic lead. Microorganisms capable of degrading tetraalkyl lead, including TEL, have not been reported. However, microbial degradation could be partially responsible for the disappearance of TRML in soil. Blais reported that themore » levels of TRML in nonsterile soil were lower than that in corresponding autoclaved soil after 24 hr of incubation. This study looks at biological and chemical transformation rates of TEL to ionic organolead forms (TREL and DEL), and mineralization rates of TEL in surface and subsurface soils. [sup 14]C-labeled TEL was used so that conversion from nonionic form to ionic form could easily be determined and evolution of CO[sub 2] from the mineralization of TEL could be measured. 17 refs., 3 figs., 2 tabs.« less