Environ. Sci. Technol. 1998, 32, 598-603 The only information on the sorption of TDA to soil was Sorption and Microbial Degradation a report by Ode (1) that a laboratory lysimeter containing TDA-contaminated soil showed no TDA in leachate after 85 of Toluenediamines and weeks of simulated rainfall. The biodegradation of TDA and Methylenedianiline in Soil under MDA has been studied for assessment of their fate both in the environment and in connection with wastewater treat- Aerobic and Anaerobic Conditions ment for production facilities using a variety of test systems. Apparently, neither 2,4- nor 2,6-TDA were biodegraded as the sole carbon sources as shown in several tests for ready WILLIAM F. COWEN,* - ANN M. GASTINGER, biodegradability (2 7). However, a variety of studies in CHRISTINE E. SPANIER, AND activated sludge have shown extensive biodegradation, JEROD R. BUCKEL especially after acclimation and in the presence of cosub- - Air Products and Chemicals, Inc., Chemicals Group, strates (8 12). In a monitoring study, Snyder (13) reported Environmental Technology, 7201 Hamilton Boulevard, an average of 96.4% removal of 2,4-TDA and 93.5% removal Allentown, Pennsylvania 18195 of 2,6-TDA in an industrial wastewater treatment plant (WWTP) with up to 20 mg/L TDA in the influent. Matsui et ROBERT E. BAILEY al. (14, 15) reported the treatment of 2,4-TDA using sludge from an operating WWTP at a large industrial complex. Bailey Associates, 4115 Elm Court, Midland, Michigan 48642 Nelson et al. (16) reported that TDA mixed with methanol and anilines in production plant still bottoms was effectively biodegraded by immobilized microbial populations in packed Three of the major diamines, 2,4-toluenediamine (2,4-TDA), bed reactors. 2,6-toluenediamine (2,6-TDA), and 4,4′-methylenedianiline The existing information on biodegradation of MDA is limited and inconsistent. MDA was reported not to be readily (4,4′-MDA), used as intermediates in the production of biodegradable (2, 4, 17). Tests for the inherent biodegrad- polyurethanes have been studied for their fate in soil. Previous ability of MDA indicate that it is biodegradable (6, 18). Ciba- literature has reported variable biodegradation of these Geigy (17) reported that there was only 6.5% removal of MDA industrially important compounds with no information on their in the Coupled Units Test, OECD 303 A, after 25 days of expected fate in soil. Their sorption to two soils and acclimation and 34 days of operation. The Coupled Units biodegradation in soil under both aerobic and anaerobic Test is a wastewater treatment simulation for determination conditions have been studied. Under aerobic and of ultimate biodegradability described by Fischer et al. (19). A bench-scale biological reactor treating a mixture of amino anaerobic conditions, sorption constants, Koc, for both isomers of TDA on loam soils were 500-1300 after8hofcontact, and nitro aromatics reduced the concentration of MDA from and the corresponding K values for MDA were 20 mg/L to less than 1 mg/L (12). Asakura et al. (10) reported oc the rapid biodegradation of MDA in the presence of aniline, 3800-5700 after8hofcontact. Both isomers of TDA and 4,4′- and they reported little reaction in the absence of aniline. MDA appear to be sorbed only a little more strongly under The only reported information on the anaerobic biodeg- 14 aerobic than anaerobic conditions. The carbon-labeled radation of either TDA or MDA is that of Krumholz et al. (20), TDA isomers and MDA started to biodegrade immediately who observed slow degradation of 2,4-TDA and 2,6-TDA after mixing with aerobic soil with the recovery of 2-3% under nitrate-reducing conditions but not under methano- 14 CO2 after only 3 days. The biodegradation slowed later genic or sulfate-reducing conditions. 14 with recovery of 11-14% CO2 after 28 days and an apparent 34-40% biodegradation after 1 year, based on Materials and Methods loss of 14C. Under anaerobic methanogenic conditions, Soil Samples. Washington silt loam surface soil was obtained 14 14 no CH4 or CO2 was recovered from any of the diamines from a farm field planted with a rotation of corn and soybeans after 71 days of incubation. near Bethlehem, PA. Freehold sandy loam surface soil was collected from the Rutgers University Experimental Farm, in Adelphia, NJ. Both of these sites are remote from any industrial activity. The soils were partially air-dried, then Introduction passed through a 2-mm sieve, and stored for 0-9 days in Toluenediamine (TDA) and methylenedianiline (MDA) are plastic bags at 4 °C until used in biodegradation tests. Sterile manufactured primarily to produce diisocyanates for use in soil subsamples for aerobic isotherm testing were prepared polyurethanes. World production of TDA, usually made as by autoclaving the sieved soil for 1 h each day, over 3 days, an 80/20 mixture of the 2,4- and 2,6-isomers, is approximately and then storing at 4 °C for 0-57 days until used. Soil 1 billion (1 × 109) kg. World production of MDA is about 1.3 properties are given in Table 1. billion kg. MDA is often made as a mixture of about 50% Test Compounds. Unlabeled 2,4-and 2,6-TDA were 4,4′-MDA with a small amount of 2,4′-MDA and the remainder obtained in the free amine form from the Air Products and oligomers. TDA and MDA are manufactured, transported, Chemicals Corporate R&D facilities (Allentown, PA). Un- and used in large volume with the possibility of their labeled 4,4′-MDA (97% purity) was obtained from Aldrich introduction to soil. This project was initiated to enable Chemical Co. (Milwaukee, WI). Uniformly 14C aromatic ring- prediction of the fate of TDA and MDA in the soil environ- labeled 2,4-TDA‚2HCl (1.9 mCi/mmol) and 2,6-TDA‚2HCl ment, where both aerobic and anaerobic processes are (1.7 mCi/mmol) were obtained from DuPont NEN (Boston, important. MA), with radiochemical purities of 99% and 94.8%, respec- tively, as determined by thin-layer chromatography (TLC). * Corresponding author telephone: 610-481-7948; fax: 610-481- Uniformly 14C aromatic ring-labeled 4,4′-MDA (free amine 4210, e-mail: [email protected]. form; 98% purity by TLC; 15.2 µCi/mg) was synthesized by 598 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 32, NO. 5, 1998 S0013-936X(97)00203-4 CCC: $15.00 1998 American Chemical Society Published on Web 01/27/1998 suspension was shaken for 24 h at 23 °C. After being shaken, TABLE 1. Summary of Test Soil Characteristics the flask was processed as described above, and the field distribution ratios for desorption (Rdesorb) were calculated CECa capacity from the solution concentration of compound and the % % % (mequiv/ TOC at 1/3 calculated diamine remaining on the soil after 24 h of soil type sand silt clay 100 g) pH (%) bar (%) desorption: Washington 21 60 19 13.6 5 1.3 23.05 ) silt loam Rdesorb (µg/g on soil)/ Freehold 53 40 7 17.7 5.8 1.6 31.46 (µg/mL of concentration in solution) sandy loam a CEC, cation exchange capacity. Anaerobic Isotherms. To examine the potential effect of oxidative reactions on the soil adsorption of TDA and MDA, isotherms were determined under anaerobic conditions. Two Amersham Life Science (Arlington Heights, IL). Stock grams of 2-mm sieved silt or sandy loam soils were weighed solutions of the TDAs were prepared in either acetone or into acid-washed, heat-sterilized glass 40-ml vials with hole- water, while the MDA stock solutions were prepared in type plastic screwcaps and Teflon-lined rubber septa. Next, 14 14 acetone. Both [1- C]- and [2- C]acetic acid, sodium salt, helium-stripped deionized water and helium-stripped 0.1 M were obtained from DuPont NEN (Boston, MA). CaCl2 solution plus sodium acetate and glucose solutions Aerobic Isotherms. Complete isotherms were deter- (stripped with 30% CO2/70% N2) were added. The total mined with autoclaved test soils in 0.01 M CaCl2 in Erlenmeyer solution volume was 35 mL minus the volumes of TDA or flasks shaken for 8 h. Isotherm sets were prepared with two MDA solutions, which were to be added later after the soils 250-mL flasks containing either2gofsoil and 35 mL of had attained anaerobic conditions (final isotherm concen- solution or5gofsoil and 35 mL of solution (for 2,4- and trations were 0.01 M CaCl2 and 0.0125 M acetate and glucose). 2,6-TDA on sandy loam) at each of six different levels of Two additional vials containing soils, CaCl2, acetate, and 14 compound concentration and known C specific activity, glucose solutions were also set up to be opened as surrogates 14 using standard mixtures containing unlabeled and C- for the other vials to determine oxidation-reduction potential labeled TDA or MDA solutions. Calcium chloride solution (ORP) conditions prior to the additions of TDA and MDA. All (0.1 M) was added to each flask plus water to give a constant of the vials were purged for 4 min with 50 cm3/min of a 30% soil/water ratio with 0.01 M CaCl2 and a range of diamine CO2/70% N2 gas mixture to remove dissolved oxygen and concentrations from 0.5 to 53 mg/L. In addition, duplicate then were capped and allowed to stand in darkness for 3-5 - flasks at the highest concentration of the series (26.2 40.2 days to allow development of anaerobic conditions. mg/L) were set up without soil as controls, and two additional After incubation, the two anaerobic surrogate vials were - sets of duplicate flasks at an intermediate concentration (8.8 opened inside an N2 atmosphere glovebag to determine their 13.8 mg/L) were set up to be shaken for 7 days, counted, and ORP, using an Orion combination platinum wire/reference then used for desorption testing (see below).