Spatialized temporal dynamics of daily ozone concentrations: Identification of the main spatial differences.

Ground-level ozone (O3) is one of the most worrisome air pollutants regarding environmental and health impacts. There is a need for a deeper understanding of its spatial and temporal dynamics. Models are needed to provide continuous temporal and spatial coverage in ozone concentration data with a fine resolution. However, the simultaneous influence of each determinant of ozone dynamics, their spatial and temporal variations, and their interaction make the resulting dynamics of O3 concentrations difficult to understand. This study aimed to i) identify different classes of temporal dynamics of O3 at daily and 9 km2 resolution over a long-term period of 12 years, ii) identify the potential determinants of these dynamics and, iii) explore the spatial distribution of the potential classes of temporal dynamics on a spatial continuum and over about 1000 km2. Thus, 126 time series of 12-year daily ozone concentrations were classified using dynamic time warping (DTW) and hierarchical clustering (study area centered on Besançon, eastern France). The different temporal dynamics obtained differed on elevation, ozone levels, proportions of urbanized and vegetated surfaces. We identified different daily ozone temporal dynamics, spatially structured, that overlapped areas called urban, suburban and rural. Urbanization, elevation and vegetation acted as determinants simultaneously. Individually, elevation and vegetated surface were positively correlated with O3 concentrations (r = 0.84 and r = 0.41, respectively), while the proportion of urbanized area was negatively correlated with O3 (r = -0.39). An increasing ozone concentration gradient was observed from urban to rural areas and was reinforced by the elevation gradient. Rural areas were both subject to higher ozone levels (p < 0.001), least monitoring and lower predictability. We identified main determinants of the temporal dynamics of ozone concentrations. The joint influence of determinants was also synthesized. This study proposed a systematic, and reproducible way to build exposure area mapping.

Improvement of downscaled ozone concentrations from the transnational scale to the kilometric scale: Need, interest and new insights.

BACKGROUND: Ground-level ozone is a major public health issue worldwide. An accurate assessment of ozone exposure is necessary. Modeling tools have been developed to tackle this issue in large areas. However, these models could present inaccuracies at the local scale. OBJECTIVES: The objective of this study was i) to assess whether O3 concentrations estimated by transnational modeling at the kilometric scale (9 km2) could be improved, ii) to propose a potential correction of these downscaled ozone concentrations and iii) to evaluate the efficiency and applicability of such a correction. METHOD: The present work was carried out in three phases. First, the performance of a transnational modeling platform (PREV'EST) was assessed at 6 geographic points by comparison with data from 6 air quality monitoring stations. Performance indicators were used for this purpose (MBE (mean bias error), MAE (mean absolute error), RMSE (root mean square error), r (Pearson correlation coefficient), and target plots). Second, several corrections were developed using MARS (multivariate adaptive regression splines) and integrating different sets of variables (mean temperature, relative humidity, rainfall amount, wind speed, elevation, and date). Their performance was evaluated. Third, external validation of the corrections was conducted using the data from six additional air quality monitoring stations. RESULTS: The uncorrected PREV'EST model presented a lack of exactitude and precision. These concentrations did not reproduce the interday variability of the measurements, leading to a lack of temporal contrast in exposure data. For the best performance enhancement, the correction applied improved MBE, MAE, RMSE and r from 14.67, 19.23, 23.18 and 0.67 to 0.00, 8.00, 10.19 and 0.91, respectively. External validation confirmed the efficiency of the corrections at the regional scale. CONCLUSIONS: We propose a validated and efficient methodology integrating local environmental variables. The methodology is adaptable according to the context, needs and data available.

A Multidisciplinary Approach for the Assessment of Origin, Fate and Ecotoxicity of Metal(loid)s from Legacy Coal Mine Tailings.

Over the course of history, the development of human societies implied the exploitation of mineral resources which generated huge amounts of mining wastes leading to substantial environmental contamination by various metal(loid)s. This is especially the case of coal mine tailings which, subjected to weathering reactions, produce acid mine drainage (AMD), a recurring ecological issue related to current and past mining activities. In this study, we aimed to determine the origin, the fate and the ecotoxicity of metal(loid)s leached from a historical coal tailing heap to the Beuveroux river (Franche-Comté, France) using a combination of mineralogical, chemical and biological approaches. In the constitutive materials of the tailings, we identified galena, tetrahedrite and bournonite as metal-rich minerals and their weathering has led to massive contamination of the water and suspended particles of the river bordering the heap. The ecotoxicity of the AMD has been assessed using Chironomus riparius larvae encaged in the field during a one-month biomonitoring campaign. The larvae showed lethal and sub-lethal (growth and emergence inhibition and delay) impairments at the AMD tributary and near downstream stations. Metal bioaccumulation and subcellular fractionation in the larvae tissues revealed a strong bioavailability of, notably, As, Pb and Tl explaining the observed biological responses. Thus, more than 70 years after the end of mining operations, the coal tailings remain a chronic source of contamination and environmental risks in AMD effluent receiving waters.

Impact assessment of legacy wastes from ancient mining activities on current earthworm community.

Mineral resource exploitation by human societies throughout history led to the deposit of mining and smelting wastes and the subsequent contamination of surrounding soils by trace metals. After several centuries, the impact of these legacy hazardous wastes may remain a cause of environmental concern, especially for indigenous soil invertebrate populations such as earthworms. Therefore, we conducted a passive biomonitoring campaign in a former metallurgical district (Vosges Mountains, eastern France). According to community descriptors, we evidenced a significant decrease of anecic and endogeic earthworm density in the former mining stations. To link these results to soil contamination and bioaccumulation levels in earthworm tissues, we propose an original modelling approach using nonlinear mixed-effects regression models. Beyond a dose-response relationship between metal internal concentrations and their levels in soils, we highlighted contrasted behaviors according to ecological groups (epianecics and endogeics most impacted). We interpreted these results in relation to some eco-physiological features without completely exclude the influence of textural characteristics of soil, especially for deep-burrowing species such as anecic strict. Nonetheless, the presence of earthworm populations currently living in highly contaminated sites and handling elevated internal concentrations raises the question of the acquisition of genetic adaptive traits and the trophic transfers of metals.