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1. Emerging investigator series: linking chemical transformations of silver and silver nanoparticles in the extracellular and intracellular environments to their bio-reactivity

   https://doi.org/10.1039/c9en00710e  

   Minghetti, Matteo; Dudefoi, William; Ma, Qing; Catalano, Jeffrey G. (October 2019, Environmental Science: Nano)

   The fish intestine is an important barrier for environmental toxicants, including metals and metal nanoparticles. Tracking chemical transformation at the interface between the intestinal epithelium and the intestinal lumen can inform us about chemicals' bio-reactivity and toxicity but is challenging due to the lack of appropriate models. To allow for such investigations, a model of the fish intestine derived from rainbow trout ( Oncorhynchus mykiss ), the RTgutGC cell line, was used. Cells were exposed to silver nitrate (AgNO 3 ) or citrate coated silver nanoparticles (cit-AgNPs) in Leibovitz's L-15 medium without amino acids and vitamins (L-15/ex), which allowed the determination of the extracellular silver species using a chemical equilibrium model. X-ray absorption spectroscopy (XAS) was used to track intracellular silver speciation. Cellular toxicity, silver accumulation, and metallothionein (MT) mRNA levels were also measured. Cells accumulated the same concentrations of silver when exposed to equimolar amounts ( i.e. 1, 5 and 10 μM) of AgNO 3 or cit-AgNPs. However, AgNO 3 was shown to be more toxic than cit-AgNPs. Intracellular silver speciation changed over time in both exposure series. After 1 hour, intracellular silver speciation was dominated by chloride complexation in both exposures. After 24 and 72 hours of exposure to cit-AgNPs, ∼7% of silver was complexed to cysteine, whereas the remaining silver was AgNPs. In cells exposed to AgNO 3 for 72 hours, 97% of Ag was complexed to cysteine. A significant increase, compared to controls, in metallothionein mRNA levels at 24 and 72 hours of exposure to AgNO 3 and cit-AgNPs can explain the formation of Ag–cysteine complexes. In summary, these data show that silver chloride species are bioavailable and that complexation to cysteine scavenges intracellular dissolved silver ions, thus preventing toxicity. Silver nanoparticles present a similar but attenuated toxic response to AgNO 3 . Thus, at least in acute exposures, existing risk assessment for dissolved silver species could be protective for nanosilver. 

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2. Assessment of Growth and Physiological Responses of Lemna minor Exposed to 4-Aminodiphenylamine, a Tire Wear Compound

   https://doi.org/10.3390/pollutants5030020  

   Kandel, Shila; Campbell, Naja’Ree; Abdulkadir, Abubakar; Moore, Kristin; Rosby, Raphyel; Hossain, Ekhtear (September 2025, Pollutants)

   4-Aminodiphenylamine (4-ADPA) is a common additive in rubber tires, known for its antioxidant properties. It plays a crucial role in enhancing tire durability by preventing issues such as drying, cracking, and degradation from prolonged exposure to environmental factors like heat, oxygen, and ozone. However, despite its advantages in extending tire lifespan, the use of 4-ADPA raises significant environmental concerns. As tires wear down, microscopic tire wear particles (TWPs) containing 4-ADPA are released into the environment with substantial leaching, contaminating the waterways. The 4-ADPA leachates pollute and pose a threat to aquatic ecosystems, affecting various forms of marine life. The current study investigates the ecotoxicological effects of 4-ADPA on the aquatic plant Lemna minor (L. minor), focusing on its impact on relative growth and physiological biomarkers. Several parameters were assessed to evaluate ecotoxicity, including frond morphology, fresh biomass, total frond number, chlorophyll content, and starch accumulation. L. minor was grown for 7 and 14 days under controlled laboratory conditions using Hoagland media with varying concentrations of 4-ADPA (10–100 μg/L), while a control group was maintained in media without 4-ADPA. The results indicate that exposure to 4-ADPA led to a dose-dependent reduction in fresh biomass, total frond number, and chlorophyll levels. Lugol’s staining revealed increased starch accumulation in the fronds after exposure to 4-ADPA. The biological effects observed in L. minor following exposure to 4-ADPA, even at environmentally relevant concentrations, demonstrate a significant ecotoxicological impact on aquatic ecosystems. Further research involving additional species and investigating the mechanisms behind 4-ADPA toxicity is recommended to better understand its long-term consequences. 

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3. The Olfactory System of Zebrafish as a Model for the Study of Neurotoxicity and Injury: Implications for Neuroplasticity and Disease

   https://doi.org/10.3390/ijms20071639  

   Calvo-Ochoa, Erika; Byrd-Jacobs, Christine (April 2019, International Journal of Molecular Sciences)

   The olfactory system, composed of the olfactory organs and the olfactory bulb, allows organisms to interact with their environment and through the detection of odor signals. Olfaction mediates behaviors pivotal for survival, such as feeding, mating, social behavior, and danger assessment. The olfactory organs are directly exposed to the milieu, and thus are particularly vulnerable to damage by environmental pollutants and toxicants, such as heavy metals, pesticides, and surfactants, among others. Given the widespread occurrence of olfactory toxicants, there is a pressing need to understand the effects of these harmful compounds on olfactory function. Zebrafish (Danio rerio) is a valuable model for studying human physiology, disease, and toxicity. Additionally, the anatomical components of the zebrafish olfactory system are similar to those of other vertebrates, and they present a remarkable degree of regeneration and neuroplasticity, making it an ideal model for the study of regeneration, reorganization and repair mechanisms following olfactory toxicant exposure. In this review, we focus on (1) the anatomical, morphological, and functional organization of the olfactory system of zebrafish; (2) the adverse effects of olfactory toxicants and injury to the olfactory organ; and (3) remodeling and repair neuroplasticity mechanisms following injury and degeneration by olfactory toxicant exposure. 

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4. Enhanced toxicity of environmentally transformed ZnO nanoparticles relative to Zn ions in the epibenthic amphipod Hyalella azteca

   https://doi.org/10.1039/C8EN00755A  

   Poynton, Helen C.; Chen, Chun; Alexander, Shaun L.; Major, Kaley M.; Blalock, Bonnie J.; Unrine, Jason M. (January 2019, Environmental Science: Nano)

   After release into the aquatic environment, engineered nanomaterials (ENMs) undergo complex chemical and physical transformations that alter their environmental fate and toxicity to aquatic organisms. Hyalella azteca are sediment-dwelling amphipods predicted to have a high exposure level to ENMs and have previously shown to be highly sensitive to ZnO nanoparticles (NPs). To investigate the impacts of environmentally transformed ZnO NPs and determine the route of uptake for these particles, we exposed H. azteca to ZnSO 4 , ZnO NPs, and environmental aged ZnO NPs which resulted in three types of particles: 30 nm ZnO–Zn 3 (PO 4 ) 2 core–shell structures (p8-ZnO NPs), micron scale hopeite-like phase Zn 3 (PO 4 ) 2 ·4H 2 O (p6-ZnO NPs), and ZnS nano-clusters (s-ZnO NPs). Treatments included freshwater, saltwater (3 ppt), and the presence of sediment, with a final treatment where animals were contained within mesh baskets to prevent burrowing in the sediment. Dissolution was close to 100% for the pristine ZnO NPs and phosphate transformed NPs, while s-ZnO NPs resulted in only 20% dissolution in the water only exposures. In the freshwater exposure, the pristine and phosphate transformed ZnO NPs were more toxic (LC 50 values 0.11–0.18 mg L −1 ) than ZnSO 4 (LC 50 = 0.26 mg L −1 ) and the s-ZnO NPs (LC 50 = 0.29 mg L −1 ). Saltwater treatments reduced the toxicity of ZnSO 4 and all the ZnO NPs. In the presence of sediment, water column concentrations of Zn were reduced to 10% nominal concentrations and toxicity in the sediment with basket treatment was similarly reduced by a factor of 10. Toxicity was further reduced in the sediment only treatments where the sediments appeared to provide a refuge for H. azteca . In addition, particle specific differences in toxicity were less apparent in the presence of sediment. Bioaccumulation was similar across the different Zn exposures, but decreased with reduced toxicity in the saltwater and sediment treatments. Overall, the results suggest that H. azteca is exposed to ZnO NPs through the water column and NP transformations in the presence of phosphate do not reduce their toxicity. Sulfidized ZnO NPs have reduced toxicity, but their similar level of bioaccumulation in H. azteca suggests that trophic transfer of these particles will occur. 

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5. Atmospheric oxidation of cyanobacterial aerosols emitted from lakes and estuaries during harmful algal blooms

   https://doi.org/10.1016/j.envpol.2025.126959  

   Jang, Myoseon; Vuong, Quang Tran; Madhu, Azad; Kim, Ganghan (November 2025, Environmental Pollution)

   Harmful algal blooms (HABs) in lakes and estuaries, caused by cyanobacteria, pose various threats to humans and the environment. Cyanobacteria produce microcystins (MCs) that make animals and people sick. Once airborne, cyanobacterial aerosols are rapidly transformed through heterogeneous reactions with atmospheric oxidants, which tend to occur much faster in air than in water. The important aspects of these transformations include the degradation of MCs and the production of reactive oxygen species (ROS) from oxidized organic matter (OM) in cyanobacterial aerosol. In this study, MCs in aerosols and water samples, collected in lakes (Lake Okeechobee, Georges Lake, and Doctors Lake) of Florida during HABs, were measured using enzyme-linked immunosorbent assay kits. Organic hydroperoxides (OHP) and the oxidative potential (OP) associated with aerosols collected at Doctors Lake were measured with 4-nitrophenylboronic acid and dithiothreitol assays, respectively. The decay of MCs and the evolution of ROS in cyanobacterial aerosols were also demonstrated in an outdoor chamber under ambient sunlight. MC concentrations (0.4–2.1 μg/L) during HAB periods were higher than the US EPA guideline (0.3 μg/L for pre-school age and 1.6 μg/L for school-age and above). Airborne MC concentrations ranged from 0.2 to 5.7 ng/m3. Regulations for airborne MC concentrations are yet to be established. In both field and chamber data, MCs decomposed but ROS substantially increased as aerosols atmospherically oxidized. Aerosolized OM concentrations during HABs were higher than those in dormant periods. OM in cyanobacterial aerosols was enriched at estuary Doctors Lake with high inorganic salt concentrations due to salting-out of water-soluble organics into lake-surface layers. Aerosolized OM concentrations were positively corelated to OP and OHP (r = 0.96 and 0.85, respectively) at Doctors Lake suggesting that cyanobacterial aerosols might adversely influence respiratory health. The longitudinal health impacts of aerosolized cyanobacteria emitted from HABs should be investigated in the future. 

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