First Evidence of the Bioaccumulation and Trophic Transfer of Tire Additives and Their Transformation Products in an Estuarine Food Web.

The discovery of the significant lethal impacts of the tire additive transformation product N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q) on coho salmon has garnered global attention. However, the bioaccumulation and trophic transfer of tire additives and their transformation products (TATPs) within food webs remain obscure. This study first characterized the levels and compositions of 15 TATPs in the Pearl River Estuary, estimated their bioaccumulation and trophic transfer potential in 21 estuarine species, and identified priority contaminants. Our observations indicated that TATPs were prevalent in the estuarine environment. Eight, six, seven, and 10 TATPs were first quantified in the shrimp, sea cucumber, snail, and fish samples, with total mean levels of 45, 56, 64, and 67 ng/g (wet weight), respectively. N,N'-Diphenyl-p-phenylenediamine (DPPD) and N,N'-bis(2-methylphenyl)-1,4-benzenediamine (DTPD) exhibited high bioaccumulation. Significant biodilution was only identified for benzothiazole, while DPPD and DTPD displayed biomagnification trends based on Monte Carlo simulations. The mechanisms of bioaccumulation and trophodynamics of TATPs could be explained by their chemical hydrophobicity, molecular mass, and metabolic rates. Based on a multicriteria scoring technique, DPPD, DTPD, and 6PPD-Q were characterized as priority contaminants. This work emphasizes the importance of biomonitoring, particularly for specific hydrophobic tire additives.

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.

Free and conjugated forms of metabolites are indispensable components of steroids: The first evidence from an estuarine food web.

Steroids have attracted particular attention as environmental contaminants because of their severe endocrine-disrupting effects. Previous studies have predominantly focused on parent steroids; however, the levels and proportions of the free and conjugated forms of their metabolites remain largely unclear, especially in food webs. Here, we first characterized the free and conjugated forms of parent steroids and their metabolites in 26 species in an estuarine food web. The steroids were dominated by their metabolites in water samples, whereas parent compounds were predominant in sediment samples. The total mean steroid concentrations in the biota samples that underwent non-enzymatic hydrolysis decreased in the following order: crabs (27 ng/g) > fish (5.9 ng/g) > snails (3.4 ng/g) > shrimps and sea cucumbers (1.2 ng/g); and those in the biota samples that underwent enzymatic hydrolysis decreased in the following order: crabs (57 ng/g) > snails (9.2 ng/g) > fish (7.9 ng/g) > shrimps and sea cucumbers (3.5 ng/g). The proportion of metabolites in the enzymatic hydrolysis biota samples was higher (38-79%) than that (2.9-65%) in non-enzymatic ones, indicating that the free and conjugated forms of metabolites in aquatic organisms were not negligible. Most synthetic steroids were either bioaccumulative or highly bioaccumulative. Importantly, in the invertebrate food web, 17α-methyltestosterone was biomagnified, while 17ß-boldenone underwent trophic dilution. Although the estuarine water had a median ecological risk level, the health risks via aquatic product consumption were very low. This study provides novel insights into the composition and trophic transfer of steroids in an estuarine food web for the first time and highlights that free and conjugated metabolites should receive more attention, particularly in biota samples.