Investigation into the partitioning of Lindane between air and dust in indoor environments
The investigation of harmful semi volatile organic compounds (SVOC) in the indoor environment is important because on average people spend over 90% of their time indoors. Lindane, an SVOC which was widely used in the UK until 2004, adsorbs to house dust. House dust acts as a reservoir for such contaminants which are remitted by desorption into the air over time. A method for measuring Lindane air concentrations in a vial using SPME without the use of water or any solvent was developed in order to carry out Lindane adsorption and desorption tests. Dynamic tests were carried out to determine adsorption and desorption coefficients as well as equilibrium time. Adsorption and desorption constants (k1 and k2 respectively) were determined by fitting results from the dynamic adsorption tests to an existing two compartment model described in chapter 2, using the statistical analysis software SPSS (vs16). These dynamic tests were carried out for two size fractions (<20µm and >45µm<63µm) and whole dust samples to determine the effect of size fraction on adsorption. For the >45µm to <63µm, k1 = 0.568h-1 and k2 = 0.047h-1, (standard error 0.119 and 0.030 respectively), for the <20µm fraction, k1 = 1.686h-1, k2 = 0.125h-1 (standard error 1.888 and 0.324 respectively), and the whole dust k1= 2.587 h-1, k2= 0.288 h-1 (standard error 0.514 and 0.113 respectively). Static tests were carried out at equilibrium to establish an adsorption isotherm and obtain partition coefficients for different size fractions. The adsorption constants Ka were 4.2 x 10-4mh-1, 7.67 x 10-5mh-1, and 3.03 x 10-3mh-1 respectively. The desorption constants Kd were 0.125h-1, 0.047h-1, 0.288h-1. The partition coefficients Kp were 4.8 x 101µgm-2, 4.08 x 101µgm-2, 1.05 x 102µgm-2, for the <20µm, >45µm<63µm, and whole dust respectively. The higher Kp value for the smaller <20µm fraction compared to the >45µm<63µm fraction, suggests that Lindane adsorbs more strongly to smaller dust size particles. This is significant because it means that the inhalable dust fractions which fall within the <20µm fraction, will have higher concentrations and therefore could potentially be more harmful as the get into the lungs. A possible explanation for the higher Ka value for the whole dust fraction over the two other smaller fractions could be because whole dust is a more complex mixture containing more fibrous substances that may have stronger affinities for Lindane than dust e.g. carpet fibres.
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