Investigation of lead-based paint contamination in residential soils within urban and suburban areas of Palmerston North City, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Earth Science at Massey University, Manawatū, New Zealand
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2020
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Massey University
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Abstract
This study investigated the concentration and distribution of lead in soil at residential properties across the city of Palmerston North, New Zealand. Samples were collected from the topsoil of 34 urban and suburban properties constructed between 1901 and 1982. Three properties were subsequently investigated in detail using a 2m grid and sampling at 0-10cm and 11-20cm depth. Samples were prepared using acid nitrate digestion as per USEPA method 3050B and total lead analysis was completed using MPAES. Soil lead concentrations were elevated above the background concentration of 46.6mg kg⁻¹ in every property investigated. There was a strong negative relationship between soil lead concentration and distance from house. There was no correlation between lead concentration and traffic volumes/density at any of the properties. There was a strong positive relationship between soil lead concentration and property age. On average, lead decreased with depth and was below the residential limit of 210mg kg⁻¹ at the 10-20cm depth in most cases with the exception of well-mixed garden soils. There was a strong relationship between construction type and soil lead concentration with weatherboard homes exhibiting significantly higher concentrations than brick or stucco clad homes of the same age. These relationships indicate a point source for lead in residential soils from the weathering of lead-based paint that has been deposited on the ground through paint degradation with time, and through the stripping and sanding of painted surfaces prior to re-painting. An estimated 511,000 homes constructed prior to 1960 in New Zealand present a significant source of potentially lead-contaminated soils. Soil lead concentrations have been directly linked to blood lead levels and emerging evidence suggests that there is no safe blood lead level, especially in children. The assessment and management of lead impacted residential soils presents a challenge for property owners, the contaminated land sector and regulators. The protection of human and environmental health is the driver behind contaminated land management and the current framework does not effectively address residential sources of pollution that may have cumulative impacts far greater than industrial source pollution.