Quantifying the Root-to-Shoot Transfer of 4,4'-Methylenedianiline Using Pressure Chamber and Intact Plant Methods

The high-production-volume chemical 4,4'-methylenedianiline (4,4'-MDA) is an aromatic amine used to manufacture 4,4'-methylenedianiline diisocyanate for polyurethane production. Based on 4,4'-MDA's octanol/water partition coefficient (K_OW ) and correlations with the transpiration stream concentration factor (TSCF), significant plant uptake and root-to-shoot transfer are predicted. However, most correlations between K_OW and TSCF were developed for neutral organics and may not be applicable for ionizable bases such as 4,4'-MDA. To investigate, TSCF values for 4,4'-MDA were measured using pressure chamber and intact plant approaches for tomato, soybean, and wheat (intact plants only). ¹⁴ C-labeled 4,4'-MDA was used to increase analytical sensitivity and facilitate measurement of distribution within plant tissues. The TSCF of ¹⁴ C-MDA determined using the pressure chamber method was 0.04 ± 0.00 for tomato and 0.17 ± 0.10 for soybean. These values were lower than predicted from log K_OW and within the range of values for ¹⁴ C-pyrene also measured in our study (0.14 ± 0.00 for tomato and 0.16 ± 0.09 for soybean). The TSCF values calculated from measurements made from intact plants grown to maturity were statistically equivalent to those obtained from the pressure chamber method for soybean and tomato. The distributions of ¹⁴ C within the three plants species were similar, with the roots > leaves ≈ stems > fruit. The log root concentration factors for 4,4'-MDA ranged from 3.68 to 4.33 for the three plant species. This finding indicates that the aromatic amine sorption to root materials is much greater than would be predicted based on its log K_OW and may be the reason for the limited root-to-shoot transfer observed in the pressure chamber and intact plant studies. Environ Toxicol Chem 2023;42:655-662. © 2023 SETAC.