Silver nanoparticles (AgNPs) are increasingly used in various commercial products. This increased use raises ecological concerns because of the large release of AgNPs into the environment. Once released, the local water chemistry has the potential to influence the environmental fates and behaviors of AgNPs. The impacts of dissolved oxygen and natural organic matter (NOM) on the dissolution and stability of AgNPs were investigated in synthetic and natural freshwaters for 7 days. In synthetic freshwater, the aggregation of AgNPs occurred due to the compression of the electric double layer, accompanied by the dissolution of AgNPs. However, once oxygen was removed, the highest dissolved Ag (Agdis) concentration decreased from 356.5 μg/L to 272.1 μg/L, the pH of the AgNP suspensions increased from less than 7.6 to more than 8.4, and AgNPs were regenerated by the reduction of released Ag+ by citrate. The addition of NOM mitigated aggregation, inhibited oxidative dissolution and induced the transformation of AgNPs into Ag2S due to the formation of NOM-adsorbed layers, the reduction of Ag+ by NOM, and the high affinity of sulfur-enriched species in NOM for Ag. Likewise, in oxygen-depleted natural freshwaters, the inhibition of oxidative dissolution was obtained in comparison with oxygenated freshwaters, showing a decrease in the maximum Agdis concentration from 137.6 and 57.0 μg/L to 83.3 and 42.4 μg/L from two natural freshwater sites. Our results suggested that aggregation and dissolution of AgNPs in aquatic environments depend on the chemical composition, where oxygen-depleted freshwaters more significantly increase the colloidal stability. In comparison with oxic conditions, anoxic conditions were more favorable to the regeneration of AgNPs by reducing species (e.g., citrate and NOM) and enhanced the stability of nanoparticles. This indicates that some AgNPs will be more stable for long periods in oxygen-deprived freshwaters, and pose more serious environmental risks than that in oxygenated freshwaters.

Acetylacetone (AcAc) has proven to be a potent photo-activator in the degradation of color compounds. The effects of AcAc on the photochemical conversion of five colorless pharmaceuticals were for the first time investigated in both pure and natural waters with the UV/H2O2 process as a reference. In most cases, AcAc played a similar role to H2O2. For example, AcAc accelerated the photodecomposition of carbamazepine, oxytetracycline, and tetracycline in pure water. Meanwhile, the toxicity of tetracyclines and carbamazepine were reduced to a similar extent to that in the UV/H2O2 process. However, AcAc worked in a way different from that of H2O2. Based on the degradation kinetics, solvent kinetic isotope effect, and the inhibiting effect of O2, the underlying mechanisms for the degradation of pharmaceuticals in the UV/AcAc process were believed mainly to be direct energy transfer from excited AcAc to pharmaceuticals rather than reactive oxygen species-mediated reactions. In natural waters, dissolved organic matter (DOM) played a crucial role in the photoconversion of pharmaceuticals. The role of H2O2 became negligible due to the scavenging effects of DOM and inorganic ions. Interestingly, in natural waters, AcAc first accelerated the photodecomposition of pharmaceuticals and then led to a dramatic reduction with the depletion of dissolved oxygen. Considering the natural occurrence of diketones, the results here point out a possible pathway in the fate and transport of pharmaceuticals in aquatic ecosystems.

Palladium (Pd) emitted from vehicles equipped with exhaust catalytic converters has been accumulating at a greater rate relative to other platinum group elements (PGE) in the last 10–20 years. Little is known, however, regarding the various environmental factors and conditions which are likely to modulate the chemical behavior and bioaccessibility of this element post-emission. To meet data needs, soils and a Pd model substance were treated with solutions containing common anions (Cl−, NO3−, SO42− und PO43−) to shed light on the geochemical behavior of emitted Pd under ambient conditions. As part of this, the particle surface chemistry of treated residues (insoluble phase) and solutions (soluble phase) was examined using XPS to assess the chemical transformation of Pd in the presence of inorganic anions. The results show that Pd is the most soluble in the presence of anionic species, followed by rhodium (Rh) and platinum (Pt). Pd in field-collected samples was found to be considerably more soluble than the metallic Pd in the model substance, Pd black, when treated with anionic species. The results also demonstrate that the solubility of Pd black is strongly dependent on solution pH, concentration and the duration of reaction. The outer 3–4 atomic layers of metallic Pd was determined via XPS to be partially oxidized when treated with anion solutions, with the degree being dependent on anion type. The concentration of dissolved O2 in solution was found to have little impact on the transformation of metallic Pd. Given the ubiquitous nature of the anions examined, we can expect that Pd will become more bioaccessible post-emission.

Hypoxia is associated with mass mortality in estuaries, but a direct causal relationship has not been proven to date. This study aimed to demonstrate this relationship and to evaluate how the duration of hypoxia affects the survival of ark shells (Anadara kagoshimensis) using mathematical modeling. The dissolved oxygen concentration was monitored at two stations in the innermost area of Ariake Bay, Japan, to calculate the duration of hypoxia. This was then included in a mathematical model to simulate the population density with sequential computation. The population density decreased with prolonged hypoxia, reaching a value close to the observed population density, indicating that hypoxia is the main cause of mass mortality in ark shells. Furthermore, the ark shell population disappeared in 8days with constant hypoxia but persisted when hypoxia was alternated with normoxia every 6 h. Therefore, mass mortality is caused by the duration rather than the frequency of hypoxia.

Shipping is a vital industry for the global economy. Stability of ships, provided by ballast water, is a crucial factor for cargo loading and unloading processes. Ballast water treatment has practical significance in terms of environmental issues, ecosystem, and human health, because ships discharge this water into the environment before loading their cargos. This study reviews the common methods for ballast water management – exchange, heating, filtration, ultrasonic treatment, ultraviolet irradiation, chemicals, and gas supersaturation – to select the best one. This study compares water temperature, salinity, dissolved oxygen, polycyclic aromatic hydrocarbons (PAHs), and heavy metals (Co, Cr, Ni, Pb) for ballast tanks of selected ships with the recipient port environment in the Persian Gulf as a case study. The exchange of ballast water in the ocean and/or its treatment on board to prevent inadvertent effects on the environment's physicochemical conditions is related to vessel characteristics, legislation, and the environmental condition. Ecological risk study showed that the salt content in ballast water is close to that of seawater, but the values of Cr (2.1mg/l) and Ni (0.029mg/l) in ballast water are higher than those in seawater (1 and 0.004mg/l, respectively).

This work is an evaluation of metal contamination degree in Phorcus turbinatus and a monitoring of metals impact on metallothioneins functioning. The gastropod was sampled from six stations along the northeastern and eastern coasts of Tunisia during four seasons (2014–2015). Our results suggested that sedimentological metallic contents (Copper, Zinc and Cadmium) vary significantly depending on stations and not significantly according to seasons except for copper. Nevertheless, differences were no significant between stations and significant between seasons as for ambient factors, metallic intrinsic contents and metallothioneins rates. The monodonta tissue seems to be enriched in the four analyzed metals (Cu, Zn, Cd and Hg) and this species seems to have an ability to accumulate metals. Metal effect on the protein induction may be linked to physicochemical factors (temperature, O2 and Cu contents in sediment). In fact, metallothioneins levels were positively correlated to the dissolved oxygen rates and negatively linked to temperature.

Failure of the Bay Park Sewage Treatment Plant (STP) during Superstorm Sandy led to adverse effects in the waters of Hempstead Bay, Long Island, NY. These appear to be related to large discharges of partially treated sewage through its primary and auxiliary outfalls. Modeled dilution discharges indicate that sewage infiltrated the bay, remaining up to 10days. Water column impacts included salinity and dissolved oxygen declines, and biological oxygen demand and nitrogen concentration increases. While the STP does not appear to have released fecal coliform, there were elevated levels of enterococci within the bay for a considerable period following the storm, probably from multiple sources.The STP's reduced functioning and associated environmental impacts, even with resilience upgrades, are not conducive to removing the bay from the list of Impaired Water Bodies. The results reinforce the need to transfer the discharge from the existing outfall to the ocean.

The organic enrichment of surficial sediments has a known effect on benthic faunal communities due largely to oxygen depletion and sulfide toxicity. Total dissolved sulfide (free S−2=H2S+HS−+S2−) concentrations in sediments are widely measured as a practical indicator of community effects. However, the standard ion selective electrode (ISE) method for free S−2 analysis can provide biased results owing to the inclusion of non-toxic mineral sulfides and the oxidation and volatilization of free S−2. A rapid field protocol was developed that alleviates these problems while also providing data on dissolved oxygen concentrations. Sediments collected near salmon aquaculture pens over cohesive and permeable substrates were analysed using the standard and new protocols. The results confirm previous conclusions of artifacts with the standard ISE method, while the dual indicator approach more accurately describes the stages, spatial extent and magnitude of sediment geochemical alterations affecting benthic communities.

Dissolved trace element concentrations (Ba, Fe, Mn, Si, Sr, and Zn) were investigated in the Haicheng River near to the Liaodong Bay in Northeast China during 2010. Dissolved Ba, Fe, Mn, and Sr showed significant spatial variation, whereas dissolved Fe, Mn, and Zn displayed seasonal variations. Conditions such as water temperature, pH, and dissolved oxygen were found to have an important impact on redox reactions involving dissolved Ba, Fe, and Zn. Dissolved Fe and Mn concentrations were regulated by adsorption or desorption of Fe/Mn oxyhydroxides and the effects of organic carbon complexation on dissolved Ba and Sr were found to be significant. The sources of dissolved trace elements were found to be mainly from domestic sewage, industrial waste, agricultural surface runoff, and natural origin, with estimated seasonal and annual river fluxes established as important inputs of dissolved trace elements from the Haicheng River into the Liaodong Bay or Bohai Sea.

A twelve year (2000−2011) study of three coastal lagoons in the Gulf of Mexico was conducted to assess the impacts of local watershed development and tropical storms on water quality. The lagoons have similar physical and hydrological characteristics, but differ substantially in the degree of watershed urban development and nutrient loading rates. In total the lagoons experienced 22 storm events during the period studied. Specifically, we examine (1) whether there are influences on water quality in the lagoons from watershed development, (2) whether there are influences on water quality in the lagoons from storm activity, and (3) whether water quality is affected to a greater degree by watershed development versus storm activity. The two urbanized lagoons typically showed higher water-column nitrate, dissolved organic nitrogen, and phosphate compared with the non-urbanized lagoon. One of the urbanized lagoons had higher water-column chlorophyll a concentrations than the other two lagoons on most sampling dates, and higher light extinction coefficients on some sampling dates. The non-urbanized lagoon had higher water-column dissolved oxygen concentrations than other lagoons on many sampling dates. Our results suggest long-term influences of watershed development on coastal water quality. We also found some evidence of significant storm effects on water quality, such as increased nitrate, phosphate, and dissolved oxygen, and decreased salinity and water temperature. However, the influences of watershed development on water quality were greater. These results suggest that changes in water quality induced by human watershed development pervade despite the storm effects. These findings may be useful for environmental management since they suggest that storms do not profoundly alter long-term changes in water quality that resulted from human development of watersheds.