Lead pollution in the New Zealand environment : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University
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Section I: The optimum conditions for the determination of lead by atomic absorption Spectrophotometry were investigated. Using the analysis line 2170A°, vegetation and soils could be analysed with satisfactory reproducibility. Lead concentrations in solution were determined in some cases at levels ten-fold higher than normal environmental (background) levels. The productivity of various analytical techniques used, in particular sample preparation, were shown to affect the analysis of lead in vegetation (leaves, barks, ring-cores) and soil samples. Section II: The effects of lead from motor-vehicle exhausts on trees growing along a busy thoroughfare in Palmerston North, New Zealand, were investigated. Analysis of tree samples (leaves, bark, trunk cores) and of soils, showed that the distribution of emitted lead was influenced by the direction of the prevailing wind. Lead levels were higher on the sides of trees facing the traffic. Measurements of lead concentrations in leaves, bark and soils, showed considerable accumulation in the vegetation at distances of about 5m from the main traffic movement. An investigation was carried out to determine the seasonal variation in lead content of tree leaves and dust samples along the thoroughfare and in the Palmerston North Square. It was found that only a gradual seasonal increase in the lead content occurred in leaves from the initial time of development to exfoliation. High lead levels in young leaves indicated a rapid accumulation of lead. A comparison of the lead content of Whatman filter papers and of leaves exposed to motor-vehicle exhausts, showed a significant difference associated with the type of surface retention mechanism. Dust samples from the Palmerston North Square showed no direct pattern of seasonal variation. Section III: The lead content of soil and vegetation along part of a State Highway passing through an uninhabited area of New Zealand was investigated. The region studied was 20 km from the nearest town and was traversed by a single highway carrying an average of 1200 motor vehicles per day (1973). The topography was fairly flat, about 1000 m above sea level, and the light volcanic soil supported vegetation less than 1 m in height. Analysis of soil and vegetation samples showed that elevated levels of lead occurred within 100 m of the edge of the highway. Close to the highway the decrease of lead levels in vegetation was approximately exponential, with the excess over background levels being halved about every 10-20 m. Accumulation of lead in soils, even within 10m of the highway, was significant only down to a depth of 5 cm. It is estimated that the total amount of lead in excess of background soil values, contained within 250 m of the roadway and within 6 cm of the surface, represented a significant proportion of the total lead emitted by all vehicles that have traversed the highway since the introduction of lead tetra-alkyls into motor fuel. Section IV: Lead concentrations in vegetation and soils were measured in the vicinity of the Tui Mine, Te Aroha, New Zealand. Lead levels in leaves of Beilschmiedia tawa reflected dispersion of wind-borne material around an ore treatment plant. Vegetation growing over an ore body show very high lead concentrations accumulated by the root systems. This mode of uptake could be easily differentiated from airborne deposition by the much lower proportion of the metal burden, which was removable by washing. Analysis of trunk core sections showed again a dissimilar pattern between air-borne deposition and accumulation of lead via the root system. With air-borne accumulation, trunk-cores showed a significant increase of levels towards the outside of the trunk. When accumulated via the root system, lead concentrations were appreciably uniform through the entire trunk. Section V: Sweet-corn plants (husks, leaves, stalks, kernels, cobs) and soils in the vicinity of a Hastings-Napier highway were analysed for lead fallout from motor vehicle exhausts. The distribution of lead was influenced by the direction of the prevailing wind and by traffic volume. Lead levels in inedible parts of the plants (leaves, husks, stalks and cobs) were ten-fold higher in plants near the roadway than in plants taken from background areas. Edible portions (kernels) were relatively low in lead. Extraction studies showed that a considerable portion of the total lead burden was present as a superficial deposit removable by washing with water. The evidence favoured air-borne lead rather than soil-borne lead as the main contributor to elevated levels of this element in plant tissues.
New Zealand, Lead, Environmental aspects, Toxicology