Assessing the Risk of Engineered Nanomaterials in the Environment: Development and Application of the nanoFate Model.

We developed a dynamic multimedia fate and transport model (nanoFate) to predict the time-dependent accumulation of metallic engineered nanomaterials (ENMs) across environmental media. nanoFate considers a wider range of processes and environmental subcompartments than most previous models and considers ENM releases to compartments (e.g., urban, agriculture) in a manner that reflects their different patterns of use and disposal. As an example, we simulated ten years of release of nano CeO2, CuO, TiO2, and ZnO in the San Francisco Bay area. Results show that even soluble metal oxide ENMs may accumulate as nanoparticles in the environment in sufficient concentrations to exceed the minimum toxic threshold in freshwater and some soils, though this is more likely with high-production ENMs such as TiO2 and ZnO. Fluctuations in weather and release scenario may lead to circumstances where predicted ENM concentrations approach acute toxic concentrations. The fate of these ENMs is to mostly remain either aggregated or dissolved in agricultural lands receiving biosolids and in freshwater or marine sediments. Comparison to previous studies indicates the importance of some key model aspects including climatic and temporal variations, how ENMs may be released into the environment, and the effect of compartment composition on predicted concentrations.

Impacts of sea level rise and climate change on coastal plant species in the central California coast.

Local increases in sea level caused by global climate change pose a significant threat to the persistence of many coastal plant species through exacerbating inundation, flooding, and erosion. In addition to sea level rise (SLR), climate changes in the form of air temperature and precipitation regimes will also alter habitats of coastal plant species. Although numerous studies have analyzed the effect of climate change on future habitats through species distribution models (SDMs), none have incorporated the threat of exposure to SLR. We developed a model that quantified the effect of both SLR and climate change on habitat for 88 rare coastal plant species in San Luis Obispo, Santa Barbara, and Ventura Counties, California, USA (an area of 23,948 km(2)). Our SLR model projects that by the year 2100, 60 of the 88 species will be threatened by SLR. We found that the probability of being threatened by SLR strongly correlates with a species' area, elevation, and distance from the coast, and that 10 species could lose their entire current habitat in the study region. We modeled the habitat suitability of these 10 species under future climate using a species distribution model (SDM). Our SDM projects that 4 of the 10 species will lose all suitable current habitats in the region as a result of climate change. While SLR accounts for up to 9.2 km(2) loss in habitat, climate change accounts for habitat suitability changes ranging from a loss of 1,439 km(2) for one species to a gain of 9,795 km(2) for another species. For three species, SLR is projected to reduce future suitable area by as much as 28% of total area. This suggests that while SLR poses a higher risk, climate changes in precipitation and air temperature represents a lesser known but potentially larger risk and a small cumulative effect from both.

Species sensitivity distributions for engineered nanomaterials.

Engineered nanomaterials (ENMs) are a relatively new strain of materials for which little is understood about their impacts. A species sensitivity distribution (SSDs) is a cumulative probability distribution of a chemical's toxicity measurements obtained from single-species bioassays of various species that can be used to estimate the ecotoxicological impacts of a chemical. The recent increase in the availability of acute toxicity data for ENMs enabled the construction of 10 ENM-specific SSDs, with which we analyzed (1) the range of toxic concentrations, (2) whether ENMs cause greater hazard to an ecosystem than the ionic or bulk form, and (3) the key parameters that affect variability in toxicity. The resulting estimates for hazardous concentrations at which 5% of species will be harmed ranged from <1 ug/L for PVP-coated n-Ag to >3.5 mg/L for CNTs. The results indicated that size, formulation, and the presence of a coating can alter toxicity, and thereby corresponding SSDs. Few statistical differences were observed between SSDs of an ENM and its ionic counterpart. However, we did find a significant correlation between the solubility of ENMs and corresponding SSD. Uncertainty in SSD values can be reduced through greater consideration of ENM characteristics and physiochemical transformations in the environment.