Plant-fluoride relationships in the vicinity of Tiwai Point aluminium smelter : A dissertation submitted in partial fulfilment of the requirement for the degree of Bachelor of Horticultural Science (Honours) at Lincoln College

Abstract

Phormium tenax and first and second year Pinus radiata foliage were collected at 21 sites from 0.4 to 21 km from the smelter. Pinus radiata was scored for mottling and both species were scored for tip necrosis. Coprosma lucida and Dicksonia squarrosa were collected from areas of low ambient fluoride concentration to assess their fluoride collecting properties. A selective fluoride ion electrode was used to calculate ppm fluoride for all samples. Five samples were also calorimetrically analysed for aluminium. Plant communities in the area were surveyed to indicate changes in composition since smelter production began in 1971.

Foliar fluoride decreased with distance to background levels within four kilometres of the smelter. At 0.4km 393, 112 and 14ppm fluoride and at 4.1 km 8.5 and 3ppm fluoride were found for second and first year Pinus radiata and Phormium tenax respectively. The species respective correlations between foliar fluoride and I/distance. r² values of 75%. 69% and 44% did not increase with the use of wind vectors. While second year accumulated more fluoride than first year Pinus radiata foliage, Pinus radiata had higher fluoride levels throughout the area. Near the smelter this could be a result of either particulate matter deposition or gaseous hydrogen fluoride uptake. Higher fluoride levels in necrotic tissue than green tissue near the smelter 206 ppm to 15ppm in Pinus radiata for example suggested gaseous uptake to be at least partly responsible. Although no correlation was found between visual symptoms and foliar fluoride levels. necrosis in foliage found within 600 metres of the smelter and sheltered from sea winds suggested fluoride induced injury.

Elevated foliar aluminium levels near the smelter, 2I80ppm at 0.4km in contrast with 810ppm at 21k, may have resulted from increased uptake from the soil as a result of solubilisation by emitted fluoride, or from particulate matter deposition on the foliage.

Visual, quadrat frequency and point intercept percent cover estimates found no evidence of fluroride induced changes in species composition when compared with earlier surveys.

These results suggest the fluoride emissions from the smelter in the short term had only low impact on the vegetation in the area.

Dicksonia squarrosa was found not to be a fluoride collector with foliar fluoride levels less than 20ppm. However in Coprosma lucida high foliar fluoride and aluminium levels, 300ppm and 1850ppm respectively, and no fluoroacetate suggest this species' fluoride collecting properties involve fluoride aluminium complexes in the soil.