MULTI-ELEMENTAL (C, H) STABLE ISOTOPE ANALYSIS AS A TOOL TO DETERMINE PHENOLIC COMPOUND FATE IN ENVIRONMENT

Phenolic compounds are priority pollutants under the Clean Water Act due to their toxicity and high water solubility. Consumption of drinking water containing low concentration of phenol (≥5 ppb) causes gastrointestinal illnesses and neurological effects in human. In water, phenols can transform by physical, chemical and microbiological processes into a mixture of products that pose even more health and environmental concerns, e.g. chlorophenols formed upon chlorination of the water. Therefore, understanding phenolic compounds degradation pathways and metabolisms is essential for a proper water and health risk assessment.

Compound-specific isotope analysis (CSIA) has become a valuable analytical technique to gain insight into reaction mechanisms of contaminants. The lighter isotopes usually react faster than heavier isotopes of the same element, and the magnitude of isotope fractionation can point to the type of biochemical reaction. In this study, we show that the major biodegradation pathways of p-cresol and phenol in water can be distinguished using a CSIA approach.

We studied the prevailing biodegradation mechanisms of phenol and p-cresol through aerobic side-chain monohydroxylation, anaerobic phosphate-dependent carboxylation and fumarate addition. We measured the degree of isotope fractionation of both carbon (¹³C/¹²C) and hydrogen (²H/¹H) during each transformation processes. For each pathway, dual-isotope approach was used: fractionation of one element is plotted against the other and the lambda (Λ) value is determined by regression. The isotope effect is strongest in the rate limiting reactions and nonfractionating processes can mask the isotope fractionation; this masking effect can be overcome by the use of Λ values. Laboratory defined values can be then compared to those from contaminated sites or biotissues and the degradation mechanism or metabolism can be inferred. Analytical approaches developed in our research can be readily incorporated into the remediation programs of the contaminated sites and biomedical researches.