Nigel G. Purchase's research while affiliated with University of Canterbury and other places

Human teeth are a readily accessible biological tissue for which the analysis of lead has been used for the classification of people in terms of their lead exposure and absorption. However, there are three significant problem areas in the interpretation of the analytical results for lead in teeth. First, the lead is not homogeneously distributed throughout the tooth; secondly, the lead levels vary with tooth type, which relates to the age of a tooth. Lastly, there are significant variations in results from different laboratories, which, in part, reflect problems with contamination, pretreatment and analytical methods. Since teeth provide an integrated historical record of a person's lead exposure they have some attractive features as biological indicators, compared with materials such as blood. But considerable care and attention to detail is necessary to obtain reliable data.

The shellfish Chione (Austrovenus) stutchburyi has been studied as a bio-indicator for lead in an estuarine environment near Christchurch, New Zealand. Over four years the mean lead level in the soft tissue was 1·16 μg g−1. The levels responded to significant rainfall events in the catchment area. Over the four years a fall in lead levels corresponded to reduced lead inputs into a river feeding the estuary. In addition to climatic and lead source changes, seasonal effects and shell size also need to be considered, as lead levels fall in the early summer and are elevated in small shellfish. The use of the shell as a bio-indicator for lead necessitates sectional and surface shell analysis rather than whole shell analysis. Both shell age and depth into the shell are variables that associate with lead.

The lead levels in the river sediments of two small rivers draining the city of Christchurch, New Zealand, reflect nearby inputs from a lead accumulator battery factory and street dust carried into the river. The high levels found in the river sediments are not reflected in the levels in the sediments of the rivers' estuary. The lead species: PbCO3, PbSO4, PbS and Pb metal were found to exist in a sediment profile, the carbonate dominating near the top and sulphide near the bottom of the profile. Only a small fraction of the lead is held by sorption on to the sediments.

Different sections of permanent teeth have been sampled and the lead levels estimated using carbon furnace AAS. Very high levels of lead (500-3400 micrograms g-1) and other trace metals (Cd, Cu, Fe and Zn) occur on the surface of the teeth, falling off rapidly a few micrometers into the teeth. Lead levels in the bulk enamel of incisors vary depending on the position within the tooth, the highest values occur on the lingual side near the gums and the lowest levels on the labial side near the tooth top. The ratio of the concentration of lead in enamel to dentine and to circumpulpal dentine was found to be 1:2:6, and within the dentine the lead levels were highest in the root dentine. The root dentine in the permanent teeth of eight, near complete or representative, sets of teeth was analysed for lead. The ratio ([Pb]tooth/[Pb]total set) decreased in the order: first molars greater than central incisors greater than lateral incisors greater than canines greater than premolars greater than second molars greater than third molars. This order inversely correlates with the age of formation or eruption of the teeth, i.e. the older teeth have the highest levels of lead in the dentine. Dentine appears to be the best material to use to estimate lead, particularly in relation to the integrated lead intake of a person. Dentine lead was determined in a small sample of deciduous teeth obtained from children living in rural areas. The levels were found to be slightly less than for children living in new housing urban areas and significantly less than for children living in older houses of urban areas.