Temporal environmental hysteresis: A definition and implications for polybrominated diphenyl ethers.

We define here "temporal environmental hysteresis" as the time lag between when a pollutant's input to the environment stops and when its concentration in the environment drops to some desired fraction of its maximum concentration. The goal of this paper is to investigate temporal environmental hysteresis for polybrominated diphenyl ethers (PBDEs), which were widely used as flame retardants in consumer goods. These compounds were taken off the North American market in two steps: At the end of 2004, the so-called Penta-BDE and Octa-BDE products were withdrawn, and at the end of 2013, the Deca-BDE product was also discontinued. We focus here on PBDE concentrations in about 700 atmospheric samples collected every 12 days from 2005 to 2018 (inclusive) at two urban sites: Chicago, Illinois, and Cleveland, Ohio. In Chicago, the concentrations of BDE-47 and 99 decreased by a factor of two every 5.9 ± 0.9 and 8.0 ± 1.4 years, respectively, but the concentrations of BDE-209 doubled every 7.6 ± 1.8 years. In Cleveland, the concentrations of BDE-47 and 99 decreased by a factor of two every 5.1 ± 0.4 and 5.7 ± 0.5 years, respectively, and the concentrations of BDE-209 decreased by a factor of two every 9.2 ± 1.6 years. The delay in all these environmental responses relative to when these compounds were removed from the market is a result of decadal scale environmental hysteresis.