A case study for orphaned chemicals: 4-methylcyclohexanemethanol (MCHM) and propylene glycol phenyl ether (PPH) in riverine sediment and water treatment processes

Abstract

There are an estimated 30,000 chemicals in commerce used in quantities >1016kg per year in the US. Unfortunately there is limited information on the chemicals partitioning and reactivity properties. These orphaned or understudied chemicals are viewed as non-hazardous but can still pose serious economic, health, environmental and societal impacts as evidenced by the January 2014 spill of 37,900L of crude-MCHM (primarily 4-methylcyclohexanemethanol) and stripped-PPH (primarily dipropylene glycol phenyl ether and propylene glycol phenyl ether) into the Elk River near Charleston, WV. Using the Elk River spill as a case study of orphaned or understudied chemicals, experiments were undertaken to evaluate the adequacy of standard approaches to emergency drinking water treatment (oxidation and sorption to activated carbons). Further available sorption models for estimating the potential of these compounds to sorb to Elk River sediments and to activated carbons in drinking water systems were investigated. The results showed that powdered activated carbon (PAC) was the most effective sorbent. The trans-MCHM isomer was found to preferentially sorb compared to cis-MCHM. For MCHM concentrations ranging from 2 to 5mgL−1 in the treatment plant, PAC concentrations of 0.1–1.4mgL−1 would be required to lower both MCHM isomers to the CDC screening level. In most cases, published linear solvation energy relationships and quantitative structure activity relationships were inadequate to estimate the a priori likelihood of sorption of MCHM and PPH to sediments and GAC, but did fit the PAC results well. Permanganate and chlorine oxidation of the compounds showed limited to insignificant removal. The studies presented herein suggest that there are still inherent vulnerabilities to drinking water treatment systems that need to be addressed.