Scrutinizing surficial sediment along a 600-km-long urban coastal zone: Occurrence and risk assessment of fipronil and its three degradates

Contamination in the coastal zone is closely linked to urbanization and has become a global issue. The coastal aquatic environment is the terminal sink for many chemicals; however, little is known about the occurrence and variation among habitats as well as integrative toxicity for pesticides, i.e., fipronil, and its three major degradates (-desulfinyl,-sulfide, and-sulfone, fiproles hereafter) in sediments in urban coastlines. In the present study, we report results of a random stratified survey for fiproles in surficial sediments in five embayment hab-itats (strata) along the Southern California Bight (SCB), USA coastline. Fiproles were present in a small areal ex -tent (6.8%) of the SCB embayment, and detected in 14 out of 174 stations with a total concentration of the four analytes ranging from 0.50 to 17.5 mu g/kg dry weight. The area-weighted mean concentrations were 3.16 +/- 3.37, 0.584 +/- 0.558, 0.071 +/- 0.103, and 0.005 +/- 0.009 mu g/kg in brackish estuaries, estuaries, bays, and marinas, respectively, with the results below the detection limits in ports. Fipronil sulfone had the greatest detection fre-quency (8.05%) and highest mean concentration (3.24 +/- 3.36 mu g/kg) among the four compounds. A screening-level deterministic risk assessment for invertebrates found that, region-wide, fiproles generally posed an insignif-icant to low acute risk to the amphipod Eohaustorius estuarius in 7.36% of the SCB embayment area. In addition, high risk to the midge Chironomus dilutus was found in 77.5% of the fiproles-detectable area in the brackish estu-ary stratum that isa part of the Los Angeles River. Fipronil sulfone was identified as the major contributor of these effects. The results of this study establish a baseline of occurrence and toxicity potential for fiproles in coastal sed-iments of southern California. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the occurrence of fiproles in sediment in five habitats along the Southern California coastline and found that fipronil sulfone was the major contributor to toxicity effects in certain areas, posing high risks to benthic organisms. These results establish a baseline for fiproles in coastal sediments in southern California.