Enantiomer-specific bioaccumulation and depuration of hexabromocyclododecanes in zebrafish (Danio Rerio)

The Developmental Toxicity and Endocrine-Disrupting Effects of Fenpropathrin on Gobiocypris rarus during the Early Life Stage

In the present study, the developmental toxicity and endocrine-disrupting effects of fenpropathrin on Gobiocypris rarus during the early life stage were studied using a semi-static water exposure method. The results showed that the LOEC (lowest observed effect concentration) of fenpropathrin on the incubation of rare minnow embryos was above 2.5 μg·L-1. The LOEC and NOEC (no observed effect concentration) of fenpropathrin on the developmental malformations and death indicators were 2.0 and 1.5 μg·L-1, respectively. After exposure to 1.5 μg·L-1 of fenpropathrin for 31 days, the expressions of androgen receptor genes (AR) and sex hormone-synthesis-related genes (CYP17 and CYP19a) were significantly decreased and the expressions of thyroid hormone receptor genes (TRβ) and aryl hydrocarbon receptor genes (AhR1a and AhR2) were significantly increased in juvenile Gobiocypris rarus. The expression levels of the androgen receptor gene (AR), estrogen receptor gene (ER1), and the sex hormone-synthesis-related genes (HMGR, CYP17, and CYP19a) were significantly decreased, while the estrogen receptor gene (ER2a), thyroid hormone receptor gene (TRβ), and aromatic hydrocarbon receptor genes (AhR1a and AhR2) were upregulated in juvenile Gobiocypris rarus under exposure to 2.0 μg·L-1 of fenpropathrin. Relatively low concentrations of fenpropathrin can affect the expression of sex hormone receptor genes, genes related to sex hormone synthesis, thyroid hormone receptor genes, and aromatic hydrocarbon receptor genes, thus interfering with the reproductive system, thyroid system, and metabolic level in Gobiocypris rarus. Therefore, more attention should be paid to the endocrine-disrupting effect caused by the pyrethroid insecticides in the water environment. Furthermore, studies on the internal mechanism of the endocrine-disrupting effect of pyrethroid insecticides on fish is needed in the future.

Tissue-specific accumulation, bioaccumulation, and depuration of liquid crystal monomers (LCMs) in adult zebrafish (Danio rerio)

This study investigated the properties of bioaccumulation, tissue-specific accumulation, and depuration of liquid crystal monomers (LCMs) in adult zebrafish (Danio rerio) exposed to a mixture of 39 LCMs for 19 days followed by depuration for 12 days. Tissue-specific accumulation of LCMs was examined at the time point of day 19, and we observed that the distribution of LCMs varied among different tissues with the following order of Σ₃₉LCM concentrations, the intestine > brain > gill > liver > muscle. We also observed that the bioaccumulation potential of LCMs varied among LCM groups with different functional groups, and LCMs with the cyan group were prone to accumulate in zebrafish. Among the 39 target LCMs, nine exhibited bioconcentration factors (BCFs) >1000, indicating their great bioaccumulation potential in aquatic environments. The experimental BCFs of 22 LCMs in the present study were lower than the theoretical values predicted by the Estimation Programs Interface (EPI) Suite software developed by U.S. Environmental Protection Agency (USEPA), suggesting that their bioaccumulation potential might be overestimated by theoretical estimation techniques. Another interesting finding was the significant positive correlation relationship in both sexes of zebrafish (p < 0.01, r² = 0.66 for male; p < 0.01, r² = 0.41 for female) between logBCF_ww and logK_ow values of LCMs. Overall, this study provides fundamental information regarding the bioaccumulation potentials of LCMs, which could be helpful for further investigating the health risks of LCMs in aquatic environments.

Concentration-dependent toxicokinetics of novel PFOS alternatives and their chronic combined toxicity in adult zebrafish

The increasing use of perfluorooctanesulfonate (PFOS) alternatives has led to their release into the aquatic environment. This study sought to determine the effects of exposure concentration on the toxicokinetics of PFOS and its alternatives, including perfluorobutanesulfonic acid (PFBS), perfluorohexanesulfonic acid (PFHxS), chlorinated polyfluorinated ether sulfonate (F-53B) and sodium p-perfluorous nonenoxybenzenesulfonate (OBS) in adult zebrafish by exposure to mixtures of the five per- and polyfluoroalkyl substances (PFAS) at 1, 10, and 100 ng/mL for 28-day, followed by a 14-day depuration. PFAS predominantly accumulated in the blood and liver, and the bioconcentration factor (BCF) decreased in the order of F-53B > PFOS > OBS ≫ PFHxS > PFBS in whole-fish homogenates. The uptake rate constants and BCF of the short-chain PFAS (≤C6) positively correlated with increasing exposure concentration, while the long-chain PFAS (≥C8) exhibited a pattern of first increasing and then decreasing. A consistent increase in the elimination rate constants of short- and long-chain PFAS was observed with increasing exposure concentration. All PFAS form tight conformations with ZSA and ZL-FABP via hydrogen bonding as revealed by molecular docking analysis. Furthermore, chronic combined exposure to PFAS induced the occurrence of vacuolation and oxidative stress in the zebrafish liver. Our findings uniquely inform the concentration-dependent bioconcentration potential and health risks to aquatic organisms of these PFOS alternatives in the environment.

The toxicokinetics and risk assessment of pyrethroids pesticide in tilapia (Oreochromis mossambicus) upon short-term water exposure

Pyrethroids pesticides (PPs) are the widely adopted synthetic pesticides for agriculture and fishery. The frequent use of these pesticides leads to the accumulation of residues in the freshwater environments in China, subsequently affecting aquatic organisms and ecosystems. However, there are few reports on the toxicological and risk assessment of aquaculture aquatic products. In this study, the uptake, depuration kinetics and potential risk to human health and ecology of fenpropathrin, cypermethrin, fenvalerate, and deltamethrin were assessed using tilapia. The results indicated that four PPs were readily accumulated by tilapia. The bioconcentration factors (BCF) of the PPs in plasma and muscle were between 71.3 and 2112.1 L/kg and 23.9-295.3 L/kg, respectively. The half-lives (t_1/2) of muscle and plasma were 2.90-9.20 d and 2.57-8.15 d. The risks of PPs residues in the muscle of tilapia and exposed water were evaluated by hazard quotient (HQ) and risk quotient (RQ). Although PPs residues in tilapia had a low dietary risk to human health, the residues in the exposed water had a high ecological risk to fish, daphnia, and green algae. Therefore, assessing the PPs content in freshwater aquaculture and monitoring their dosages and frequencies are highly necessitated to avoid their adverse effect on the aquaculture environment.

Enantioselective Bioaccumulation of the Chiral Insecticide Indoxacarb in Zebrafish (Danio rerio)

Indoxacarb is a typical chiral insecticide widely used in agricultural pest control. In the present study, zebrafish was used as a model animal to explore the enantioselective bioaccumulation behavior of indoxacarb to nontarget species in aquatic environments. Zebrafish were exposed to 0.025 and 0.1 mg/L rac-indoxacarb solution for 12 d under the semistatic method, and the bioconcentration factor (BCF) and enantiomeric fraction of zebrafish were investigated. The results showed that the (-)-R-indoxacarb preferentially accumulated in zebrafish. The BCF values at 0.025 mg/L exposure levels were 1079.8 and 83.4 L/kg for (-)-R-indoxacarb and (+)-S-indoxacarb after 12 d, respectively. The BCF values at 0.1 mg/L exposure levels were 1752.1 and 137.0 L/kg for (-)-R-indoxacarb and (+)-S-indoxacarb after 10 d, respectively. The half-life values of (-)-R-indoxacarb and (+)-S-indoxacarb were 3.47 and 2.05 d for 0.025 mg/L concentration exposure and 4.95 and 2.66 d for 0.1 mg/L concentration exposure, respectively. The enantiomeric fraction values were in the range of 0.48 to 0.55 and 0.89 to 1.00 for water and zebrafish samples, respectively. Studies on the enantioselective bioaccumulation behavior of indoxacarb will provide data for assessing the environmental fate and potential toxic effects of indoxacarb on aquatic organisms. Environ Toxicol Chem 2021;40:1007-1016. © 2020 SETAC.

Ecotoxicity of pesticides and semiochemicals used for control and prevention of conifer bark beetle (Dendroctonus spp.) outbreaks

Application of pyrethroid pesticides and semiochemicals are two treatments used worldwide to control conifer bark beetles (Dendroctonus spp.); their residues can reach water reservoirs and water currents through run off and affect non-target organisms such as freshwater invertebrates. Therefore, we assessed the 48-h lethal toxicity, chronic toxicity (reproduction inhibition), and bioaccumulation of three pyrethroid pesticides (bifenthrin, cypermethrin, and deltamethrin) and two semiochemicals (verbenone and 3-methyl-2-cyclohexen-1-one) in two freshwater invertebrates: the cladoceran Alona guttata and the rotifer Lecane papuana. Bifenthrin was the most toxic of the five chemical compounds tested followed by deltamethrin and then cypermethrin, which was the least toxic pyrethroid for both species. Semiochemicals were far less toxic than pyrethroids and verbenone was most toxic than 3-methyl-2-cyclohexen-1-one for both species. For the rotifer Lecane papuana, the pyrethroid with the highest Bioconcentration Factor was bifenthrin, and for the semiochemicals it was 3-methyl-2-cyclohexen-1-one. For the cladoceran Alona guttata, the pyrethroid with the highest bioconcentration factor was cypermethrin and for the semiochemicals it was verbenone. The pyrethroid with highest body burdens both lethal and chronic was cypermethrin. Semiochemicals showed lethal and chronic body burdens 12-fold higher than pyrethroids and were therefore less toxic than pyrethroids. These results showed that the semiochemicals verbenone and 3-methyl-2-cyclohexen-1-one are a safe tool for the freshwater invertebrates tested when compared with pyrethroid pesticides. Cypermethrin was the least toxic of the pyrethroids tested and therefore could be considered as a good candidate to control outbreaks of the conifer bark beetle.

Atmospheric concentrations of hexabromocyclododecane (HBCDD) diastereomers in the Great Lakes region

The concentrations of α-, β-, and γ-hexabromocyclododecane (HBCDD) diastereomers in atmospheric particle phase samples were determined at four United States Integrated Atmospheric Deposition Network (IADN) sites located in the North American Great Lakes basin collected between 1 January and 31 December 2014. The concentrations ranged from 0.37 to 8.9 pg/m³, 0.12-4.0 pg/m³, and 0.26-22 pg/m³ for α-, β-, and γ-HBCDD, respectively among the four sampling sites. The median ΣHBCDD concentrations for the four sites were 2.0 pg/m³, 2.1 pg/m³, 1.7 pg/m³ and 5.2 pg/m³ for Chicago, Cleveland, Sturgeon Point and Sleeping Bear Dunes, respectively. Higher levels of ∑HBCDD were observed at the remote site of Sleeping Bear Dunes with comparable levels at the remaining three sites. α-HBCDD and γ-HBCDD were the dominant isomers with an average contribution of about 40% and 50% to ΣHBCDD concentrations, respectively. These HBCDD concentrations were compared with the levels of other brominated flame retardants measured in these samples, including polybrominated diphenyl ethers (PBDEs), 2,3,4,5-tetrabromoethylhexyl benzoate (EHTBB), bis(2-ethylhexyl) tetrabromophthalate (BEHTBP), and decabromodiphenylethane (DBDPE). ∑HBCDD concentrations were significantly lower than or indistinguishable from those of PBDEs, EHTBB, BEHTBP, and DBDPE at all sites except Sleeping Bear Dunes. No significant correlations were found between ΣHBCDD and ΣPBDE, EHTBB, BEHTBP, and DBDPE concentrations, suggesting a different source of HBCDD contamination. This is the first study reporting concentrations of HBCDD isomers in the Great Lakes ambient air, and our results indicate that HBCDD is ubiquitous in the Great Lakes basin, including at remote sites.

Releasing of hexabromocyclododecanes from expanded polystyrenes in seawater -field and laboratory experiments

Expanded polystyrene (EPS) is a major component of marine debris globally. Recently, hazardous hexabromocyclododecanes (HBCDDs) were detected in EPS buoys used for aquaculture farming. Subsequently, enrichment of HBCDDs was found in nearby marine sediments and mussels growing on EPS buoys. It was suspected that EPS buoys and their debris might be sources of HBCDDs. To confirm this, the release of HBCDDs from EPS spherules detached from a buoy to seawater was investigated under field (open sea surface and closed outdoor chambers with sun exposure and in the dark) and laboratory (particle-size) conditions. In all exposure groups, initial rapid leaching of HBCDDs was followed by slow desorption over time. Abundant release of HBCDDs was observed from EPS spherules exposed to the open sea surface (natural) and on exposure to sunlight irradiation or in the dark in controlled saline water. Water leaching and UV-light/temperature along with possibly biodegradation were responsible for about 37% and 12% of HBCDDs flux, respectively. Crumbled EPS particles (≤1 mm) in samples deployed on the sea surface for 6 months showed a high degree of weathering. This implies that surface erosion and further fragmentation of EPS via environmental weathering could enhance the leaching of HBCDDs from the surface of EPS. Overall, in the marine environment, HBCDDs could be released to a great extent from EPS products and their debris due to the cumulative effects of the movement of large volumes of water (dilution), biodegradation, UV-light/temperature, wave action (shaking), salinity and further fragmentation of EPS spherules.

Tissue Distribution and Transfer to Eggs of Ingested α-Hexabromocyclododecane (α-HBCDD) in Laying Hens (Gallus domesticus)

The aim of the current study was to describe the fate of ingested α-hexabromocyclododecane (α-HBCDD) in laying hens. Individuals were exposed to two dietary concentrations of α-HBCDD (50 and 5 ng g(-1) feed) for 18 or 11 weeks followed by a 7-week decontamination period. The results show that no isomerization of α- to β- or γ-HBCDD forms occurred, whereas OH-HBCDD was identified as a product of α-HBCDD metabolism. Irrespective of the level of feed contamination, estimates of steady-state accumulation ratios were 5.2, 3.6, and 9.2 and half-lives were estimated at 17.4, 22.8, and 35.3 days in egg yolk, liver tissue, and abdominal fat, respectively. The steady-state carry-over rate to eggs was 22.9%. Thus, α-HBCDD ingested by laying hens is readily transferred to eggs and significantly accumulates in adipose tissue.

Hexabromocyclododecane in polystyrene based consumer products: an evidence of unregulated use

Polystyrene (PS) is made flame retardant by combining with hexabromocyclododecane (HBCD). HBCD can release from consumer products during their production, use or disposal. As a result, it has become a ubiquitous contaminant in the environment with a high potential for bioaccumulation. Therefore, to evaluate the extent of exposure to HBCD from PS, we determined the concentration of HBCD in a variety of products (n=34) made from three types of commonly used PS: expanded PS (EPS), extruded PS foam (XPS), and extruded PS. The concentration of HBCD was highest in EPS, with a mean value and range of 475643±16710ngg(-1) and 106-960000ngg(-1), respectively. PS related to building construction and laboratory uses had a significantly higher concentration of HBCD (3300-905000ngg(-1)), except XPS styroboard (191±100ngg(-1)). Lower concentrations were measured in most food-related products (24.3-199ngg(-1)). However, a relatively high concentration of HBCD was detected in an ice box (960000±29000ngg(-1)), aquaculture buoy (53500±2100ngg(-1)), and disposable tray (8430±730ngg(-1)) used in fish market, raising concern for public health. Our data demonstrate a wide variation in the concentration of HBCD, suggesting a lack of proper controls for the addition of HBCD to PS products. Other brominated flame retardants (BFRs) were also detected in a majority of the XPS products (TBBPA=3.83-545ngg(-1), BTBPE=44-216ngg(-1) and DBDPE=215-4200ngg(-1)). Thus, HBCD is being added to PS along with other BFRs that cannot be ignored.

Dynamics of uptake and elimination of pyrethroid insecticides in zebrafish (Danio rerio) eleutheroembryos

Synthetic pyrethroids (SPs) are among the most heavily used insecticides for residential and agricultural applications. Their residues have frequently been detected in aquatic ecosystems. Despite their high aquatic toxicity, their toxicokinetics are still unclear. In this study, the kinetics of uptake and depuration of three SPs, permethrin (PM), bifenthrin (BF) and λ-cyhalothrin (λ-CH), were determined for the first time using zebrafish eleutheroembryo assays. The diastereoisomer selectivity of PM in eleutheroembryos was further examined. The results indicated that three SPs were quickly taken up by eleutheroembryos. The bioaccumulation factors of the SPs ranged from 125.4 to 708.4. The depuration of SPs in zebrafish eleutheroembryos followed the first-order process. The elimination rate constants (k2) of SPs in eleutheroembryos ranged from 0.018 h(-1) to 0.0533 h(-1). The half-lives (t1/2) were in the range 13.0-38.5h. The diastereoisomer fraction (DF) values for PM in the eleutheroembryos estimated at different uptake and depuration times were all significantly greater than the original value (DF=0.43), indicating selective enrichment and elimination of cis-PM relative to trans-PM. These results reveal a high capacity for SP bioconcentration by zebrafish eleutheroembryos, suggesting that SPs possess a highly cumulative risk to fish.