Diffuse anthropogenic and naturally mercury‐enriched areas represent long‐lived sources of elemental mercury to the atmosphere. The Nevada Study and Tests of the Release of Mercury From Soils (STORMS) project focused on the measurement of mercury emissions from a naturally enriched area. During the project, concurrent measurements of mercury fluxes from naturally mercury‐enriched substrate were made September 1–4, 1997, using four micrometeorological methods and seven field flux chambers. Ambient air mercury concentrations ranged from 2 to nearly 200 ng m⁻³ indicating that the field site is a source of atmospheric mercury. The mean daytime mercury fluxes, during conditions of no precipitation, measured with field chambers were 50 to 360 ng m⁻² h⁻¹, and with the micrometeorological methods were 230 to 600 ng m⁻² h⁻¹. This wide range in mercury emission rates reflects differences in method experimental designs and local source strengths. Mercury fluxes measured by many field chambers were significantly different (p<0.05) but linearly correlated. This indicates that field chambers responded similarly to environmental conditions, but differences in experimental design and site heterogeneity had a significant influence on the magnitude of mercury fluxes. Data developed during the field study demonstrated that field flux chambers are ideal for assessment of the physicochemical processes driving mercury flux and development of an understanding of the magnitude of the influence of individual factors on flux. In general, mean mercury fluxes measured with micrometeorological methods during daytime periods were nearly 3 times higher than mean fluxes measured with field flux chambers. Micrometeorological methods allow for derivation of a representative mercury flux occurring from an unconstrained system and provide an assessment of the actual magnitude and variability of fluxes occurring from an area.

Solubility is a critical component of physicochemical characterisation of engineered nanomaterials (ENMs) and an important parameter in their risk assessments. Standard testing methodologies are needed to estimate the dissolution behaviour and biodurability (half-life) of ENMs in biological fluids. The effect of pH, particle size and crystal form on dissolution behaviour of zinc metal, ZnO and TiO₂ was investigated using a simple 2 h solubility assay at body temperature (37 °C) and two pH conditions (1.5 and 7) to approximately frame the pH range found in human body fluids. Time series dissolution experiments were then conducted to determine rate constants and half-lives. Dissolution characteristics of investigated ENMs were compared with those of their bulk analogues for both pH conditions. Two crystal forms of TiO₂ were considered: anatase and rutile. For all compounds studied, and at both pH conditions, the short solubility assays and the time series experiments consistently showed that biodurability of the bulk analogues was equal to or greater than biodurability of the corresponding nanomaterials. The results showed that particle size and crystal form of inorganic ENMs were important properties that influenced dissolution behaviour and biodurability. All ENMs and bulk analogues displayed significantly higher solubility at low pH than at neutral pH. In the context of classification and read-across approaches, the pH of the dissolution medium was the key parameter. The main implication is that pH and temperature should be specified in solubility testing when evaluating ENM dissolution in human body fluids, even for preliminary (tier 1) screening.