Translocation and metabolism of tricresyl phosphate in rice and microbiome system: Isomer-specific processes and overlooked metabolites

Tricresyl phosphate (TCP) is extensively used organophosphorus flame retardants and plasticizers that posed risks to organisms and human beings. In this study, the translocation and biotransformation behavior of isomers tri-p-cresyl phosphate (TpCP), tri-m-cresyl phosphate (TmCP), and tri-o-cresyl phosphate (ToCP) in rice and rhizosphere microbiome was explored by hydroponic exposure. TpCP and TmCP were found more liable to be translocated acropetally, compared with ToCP, although they have same molecular weight and similar Kow. Rhizosphere microbiome named microbial consortium GY could reduce the uptake of TpCP, TmCP, and ToCP in rice tissues, and promote rice growth. New metabolites were successfully identified in rice and microbiome, including hydrolysis, hydroxylated, methylated, demethylated, methoxylated, and glucuronide-products. The methylation, demethylation, methoxylation, and glycosylation pathways of TCP isomers were observed for the first time in organisms. What is more important is that the demethylation of TCPs could be an important and overlooked source of triphenyl phosphate (TPHP), which broke the traditional understanding of the only man-made source of toxic TPHP in the environment. Active members of the microbial consortium GY during degradation were revealed and metagenomic analysis indicated that most of active populations contained TCP-degrading genes. It is noteworthy that the strains and function genes in microbial consortium GY that responsible for TCP isomers' transformation were different. These results can improve our understanding of the translocation and transformation of organic pollutant isomers in plants and rhizosphere microbiome.

Automated summary

Tricresyl phosphate (TCP) is commonly used as a flame retardant and plasticizer, but it poses risks to organisms and humans. This study investigated the translocation and biotransformation of three isomers of TCP in rice and rhizosphere microbiome. The results showed that TpCP and TmCP were more likely to be translocated in rice compared to ToCP. The rhizosphere microbiome was found to reduce the uptake of TCP isomers in rice and promote rice growth. New metabolites were identified in rice and microbiome, including hydrolysis, hydroxylation, methylation, demethylation, methoxylation, and glucuronidation products. It was also discovered that demethylation of TCPs can be an important source of triphenyl phosphate (TPHP) in the environment, which challenges the traditional understanding that TPHP is only man-made. The microbial consortium GY was revealed as an active member in TCP degradation, with different strains and function genes responsible for the transformation of TCP isomers. These findings enhance our understanding of the translocation and transformation of organic pollutant isomers in plants and rhizosphere microbiome.