Historical monitoring of heavy metals in kahikatea ring wood in Christchurch, New Zealand

Abstract

Tree ring wood was sampled from kahikatea trees in urban Christchurch, New Zealand, and from a background area on the west coast of South Island, New Zealand. The elements lead, cadmium, zinc, copper and manganese were analyzed in the wood using atomic absorption spectroscopy. Comparisons between the concentrations of the metals in the urban and background tree ring wood indicate a significant increase in lead, copper, zinc and cadmium since around 1860-70 for the urban trees. This can be accounted for by the start of urbanization and industrialization in Christchurch with the arrival of settlers from the United Kingdom. In the case of lead, a further increase occurred around 1950 corresponding to the escalating use of the motor car and leaded petrol. Manganese levels tended to fall from the late 19th century and may be associated with the draining of the swampy land in the city. It is suggested that the lead and cadmium in the trees mainly came from the incorporation of aerosol trapped by the bark, whereas the other three metals were probably mainly derived from the soil.