Insights into cork weathering regarding colour, chemical and cellular changes in view of outdoor applications.

A comprehensive analysis of outdoor weathering and soil burial of cork during 1-year experiments was carried out with measurements of CIELAB color parameters, cellular observations by scanning electron microscopy, and surface chemical features analysed by ATR-FTIR and wet chemical analysis. Cork applied in outdoor conditions above and below ground retained its physical structure and integrity without signs of deterioration or fracturing. The cellular structure was maintained with some small changes at the one-cell layer at the surface, featuring cellular expansion and minute cell wall fractures. Surface color and chemistry showed distinct results for outdoor exposure and soil burial. The weathered cork surfaces acquired a lighter color while the soil buried cork surfaces became darker. With outdoor weathering, the cork polar solubles increased (13.0% vs. 7.6% o.d. mass) while a substantial decrease of lignin occurred (about 28% of the original lignin was removed) leading to a suberin-enriched cork surface. The chemical impact on lignin is therefore responsible for the surface change towards lighter colors. Soil-burial induced hydrolysis of ester bonds of suberin and xylan, and the lignin-enriched cork surface displayed a dark brown color. FTIR and wet chemical results were consistent. Overall cork showed a considerable structural and physical stability that allows its application in outdoor conditions, namely for building façades or other surfacing applications. Architects and designers should take into account the color dynamics of the cork surfaces.

Bioavailability and ecological risks of trace metals in bottom sediments from Doce river continental shelf before and after the biggest environmental disaster in Brazil: The collapse of the Fundão dam.

The present study deals with bioavailability of trace metals in the Doce river continental shelf, southeast of Brazil. The bottom sediments of the study area were firstly sampled a few weeks before the biggest environmental disaster of Brazil, the collapse of the Fundão dam in November of 2015. The disaster released around 40 Mm3 of iron ore tailings into Doce river basin and an estimate of 10 Mm3 reached the river delta, having the adjacent continental shelf as the final destination. One year and a half later, on April of 2017, the continental shelf was sampled again. A total of 48 stations were evaluated concerning concentrations of trace metals (Zn, Cu, Pb, Ni, Cr) and other ancillary variables before and after the accident. Trace metals were determined through fractionation in order to assess mobility and establish the ecological risk through RAC index. Before the accident, trace metals mobility was Pb > Ni > Cu > Zn > Cr, with Pb Cu, Ni and posing high ecological risk (RAC>30%) in many stations. Differences in concentrations of metal from pre to post accident were significant, and the increase of trace metals was observed. The mobility order after the accident changed to: Cu > Pb > Ni > Zn > Cr. Metal fractionation showed remarkable changes after the accident, with elements such as Cu, Ni and Zn highly associated with reducible fractions originated from the tailings composition. Despite the decrease of RAC to medium risk after the accident in most stations, the bioavilability of Cu, Pb, Ni and Zn increased as show by their higher accumulation in the bioavailable fractions.