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Abstract
Organophosphate esters (OPEs) are used as flame retardants and plasticizers in a wide
range of consumer products. Nevertheless, studies on the occurrence and inventory
of OPEs in sewage sludge are limited. In this study, 20 OP triesters and 11 diesters
were measured in 75 archived sewage sludge samples collected from 67 wastewater treatment
plants (WWTPs) across the United States (US). The median concentrations of ∑ 20 OP-triesters
and ∑ 11 OP-diesters in sludge were 1,290 and 78.4 ng/g dry weight (dw), respectively.
Sludge samples originating from the Western and Northeastern US contained higher concentrations
of OP triesters than did those from the Midwestern and Southern US. Sludge samples
from WWTPs with larger treatment capacity (>38 million liters per day) contained higher
concentrations of OP diesters ( p <0.05). OP diesters in sludge originated from two
sources, triester degradation and direct inputs. Land application of sludge to US
soils was estimated to result in annual mass inputs of 12,400–14,900 kg/year of OP
triesters and 663–796 kg/year of OP diesters. A hazard assessment was performed for
14 OPEs found in sludge, which suggested a low level of risk from OPs at the current
land application practices of sludge.