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The aim of this study is to explore the use of lichens as biomonitors of the impact of nickel mining and ore treatment on the atmosphere in the New Caledonian archipelago (South Pacific Ocean); both activities emitting also Co, Cr and possibly Fe. Metal contents were analysed in thirty-four epiphytic lichens, collected in the vicinity of the potential sources, and in places free from known historical mining. The highest Ni, Co, and Cr concentrations were, as expected, observed in lichens collected near ore deposits or treatment areas. The elemental composition in the lichens was explored by multivariate analysis, after appropriately transforming the variables (i.e. using compositional data analysis). The sample score of the first principal component (PC1) makes the largest (positive) multiplicative contribution to the log-ratios of metals originating from mining activities (Ni, Cr, Co) divided by Ti. The PC1 scores are used here as a surrogate of pollution levels related to mining and metallurgical activity. They can be viewed as synthetic indicators mapped to provide valuable information for the management and protection of ecosystems or, as a first step, to select locations where air filtration units could be installed, in the future, for air quality monitoring. However, as this approach drastically simplifies the problem, supplying a broadly efficient picture but little detail, recognizing the different sources of contamination may be difficult, more particularly when their chemical differences are subtle. It conveys only relative information: about ratios, not levels, and is therefore recommended as a preliminary step, in combination with close examination of raw concentration levels of lichens. Further validation using conventional air-monitoring by filter units should also prove beneficial.

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<div class="page" title="Page 2"> <div class="section"> <div class="layoutArea"> <div class="column"> <p>We have examined the distribution and spectiation mercury and trace metals under contrasted season, river flow conditions and tidal amplitudes with a series of  cruises taking place between 2012 and 2015. Our laboratory had alredy undertaken a similar study in the early 1990's. The latest data acquisition efforts are an opportunity to examine the changes that occurred within that time span for mercury and its species, and to discuss the causes of the observed changes. In particular, we will replace the  observations in the perspectives of environmental regulation, and of field and laboratory practices observed for environmental chemical characterization.</p> <p>Early 1980's estuarine transects show total dissolved Hg levels near 5nM in the Loire river (Frenet, 1981). In the early 1990's, a careful and detailed study shows estuarine levels between 1 and 6pM (Coquery, 1994) with a strong dependency on the hydrological regime. New results confirm the riverine clevels in the low pM range. Concentrations decrease progressively during mixing with seawater and the oceanic end-member concentrations are near 0.5pM. Monitoring of mercury levels and speciation in the Loire river and the upper reaches of the estuary show that these Hg levels and species fluctuate with water flow and areal flooding upstream, AND on the history of that hydrological regime.</p> </div> </div> </div> </div>