New insight into the bioaccumulation and trophic transfer of free and conjugated antibiotics in an estuarine food web based on multimedia fate and model simulation

The substantial utilization of antibiotics causes their "pseudo-persistence" in offshore environments. Published studies on antibiotic surveillance in food webs have primarily emphasized on parent forms; however, the compositions and concentrations of conjugated antibiotics in aquatic organisms remain largely unexplored. This study systematically examined the distribution characteristics and trophodynamics of free antibiotics and their conjugated forms in an estuarine food web. Total antibiotic levels differed insignificantly between the surface and bottom waters. The total mean values of free antibiotics in crabs, fish, shrimps, sea cucumbers, and snails varied from 0.77 to 1.4 ng/g (wet weight). The numbers and values of antibiotics rose in these biological samples after enzymatic hydrolysis. Conjugated antibiotics accounted for 23.8-76.9% of the total antibiotics in the biological samples, revealing that conjugated forms play a non-negligible role in aquatic organisms. More number of antibiotics exhibited bioaccumulation capabilities after enzymatic hydrolysis. In the food web, the free forms of anhydroerythromycin and conjugated forms of trimethoprim and ciprofloxacin underwent trophic dilution, whereas the free forms of trimethoprim and conjugated forms of ofloxacin underwent trophic amplification. The present work provides new insights into the bioaccumulation and trophic transfer of free and conjugated antibiotics in food webs.

Per- and Poly-fluoroalkyl Substances (PFAS) in Sediment: a Source of PFAS to the Food Web?

Kent Lake is an impoundment of the Huron River in southeast lower Michigan. Fish collected from Kent Lake in 2017 had high concentrations of perfluorooctane sulfonate (PFOS) in fillets which resulted in a fish consumption advisory from the Michigan Department of Health and Human Services (MDHHS). In June 2018, a major source of PFOS was identified as the City of Wixom's wastewater treatment plant (WWTP) which discharges treated effluent to Norton Creek and the Huron River 5 miles upstream of Kent Lake. An industrial facility, which has been in operation since approximately 2000, was found to be the source of high levels of PFOS to Wixom's sanitary sewer. A granular activated carbon (GAC) system was installed at the facility, resulting in substantial reductions in PFOS concentrations in surface water and fish from Kent Lake. However, the PFOS decline in fish tissue reached a plateau at a level exceeding the "Do Not Eat" advisory threshold. This case study sought to explore the supposition that sediment is acting as an ongoing source of PFAS to the Kent Lake food web. We sampled PFAS in biota, sediment and water from Kent Lake and a nearby reference lake in 2021. Biota (benthos, forage fish and predator fish) were collected from both lakes and analyzed as whole-body composites for PFAS analytes. The results, including the patterns of PFAS contamination between the water, sediment and biota samples as well as partition coefficients and bioaccumulation factors, are consistent with PFAS in sediment acting as an ongoing source of contamination to the biota in Kent Lake. This study's results for PFOS (the predominant PFAS in Kent Lake sediment and biota) and 6:2 fluorotelomer sulfonic acid (6:2 FTS) provide additional lines of evidence that sediment acts as a source of PFAS to the aquatic food web.