Chemical changes in the stem matrix of three tree species exposed to fluoride emissions from an aluminum smelter

Abstract

The principal objective of this study was to investigate the major organic and trace elemental composition of the stem tissues of three tree species of a mixed forest on Cornwall Island in the St. Lawrence River, Ontario. This forest was exposed to atmospheric hydrogen fluoride (HF) at levels > 71 μg F/m3/24 h from an aluminum smelter (Reynolds Metals Co. Ltd.) for twenty years, followed by fourteen years of reduced emissions (< 40 μg F/m3/24 h), which is still greater than the current Ontario air quality criterion for HF (0.36 μg F/m3/24 h). Increment cores were collected at breast height from white pine, red oak, and American beech from the study woodlot on Cornwall Island and at a control site in Long Sault Provincial Park.Tree-rings were analyzed for eight elements (fluorine, aluminum, manganese, magnesium, calcium, sodium, chlorine and potassium) and some major organic compounds (total extractives, lignin and holocellulose). All three species from the study woodlot showed significant chemical compositional changes during the peak pollution and post-abatement periods. There was a substantial increase of the levels of total extractives (up to 167%), lignin (up to 38%), fluorine, aluminum and manganese and a significant decrease of holocellulose content (up to 17%) in the stem tissues during the period of HF exposure, compared to the pre-pollution period. In contrast, trees from the control site showed no significant change in chemical composition in any of the three periods. Lower cellulose and higher lignin and extractives concentrations potentially makes the wood weaker and less suitable for dimension lumber and pulping. Key words: hydrogen fluoride, extractives, lignin, holocellulose, trace elements