Abstract
Atmospheric monitoring and the determination of geographic sources of semi-volatile organic contaminants (SOC) are becoming increasingly important given the ability of SOCs to volatilise, undergo long-range atmospheric transport and accumulate in cold remote ecosystems.
Pine needles are an ideal matrix for the long-term monitoring of SOCs in the atmosphere because they are naturally occurring and distributed worldwide. However, typical extraction methods result in the co-elution of lipids and thus require time-consuming clean-up techniques. Recently, selective pressurised liquid extraction (PLE) has been used to selectively extract SOCs from various matrices without the co-elution of matrix-interfering compounds such as lipids. A selective PLE method for extracting current-use pesticides, historic-use pesticides and polychlorinated biphenyls (PCBs) from pine needles is outlined. The selective extraction was achieved by packing the extraction vessel with a fat retainer, Florisil, down-stream of the pine needle matrix. A fat to fat-retainer ratio of 0.0057 (corresponding to 35 g of Florisil per 10 g of pine needle sample) was selected to minimise the co-elution of matrix-interfering compounds. Three 5-minute extractions were performed using 25:75 (v/v) dichloromethane:n-hexane and a solvent flush of 150%. The mean recovery of current-use pesticides, historic-use pesticides and PCBs using this method was 63%, 71%, and 95%, respectively.
First- and second-year pine needles were collected at 16 sites located along a transect that crossed the Southern Alps of New Zealand. The concentrations of current- and historic-use pesticides were measured in second-year needles. Octanol-air partition coefficients and the atmospheric temperature at each site were used to calculate the theoretical concentrations of pesticides in the atmosphere. Pesticide concentration profiles were constructed for each site by normalising the measured pesticide concentrations by the sum of all pesticide concentrations. Pesticides concentration profiles based on both needle and theoretical air concentrations at each of the sites were used to determine the influence of west and east coast sources on each of the six mountain sites. The global-scale northwesterly winds were the primary influence on the pesticide burden at the two highest elevation mountain sites. The small-scale westerly upslope winds had little influence at any of the mountain sites whereas the easterly upslope winds had progressively more influence at the mountain sites closest to the east.
An approach using trace elements in particulate matter (PM) to identify the geographic sources of atmospherically transported SOCs was also investigated. Daily samples of PM and SOCs were collected with high-volume air samplers from 16 January to 16 February 2009 at Temple Basin, a remote alpine site in New Zealand’s Southern Alps. For each sampling day, the relative contribution of PM from regional New Zealand versus long-range Australian sources was determined using trace element profiles and a binary mixing model. The PM approach was used to determine that endosulfan I, indeno[1,2,3-c,d]pyrene and benzo[g,h,i]perylene found at Temple Basin were largely of Australian origin. The PM approach was also compared to two previously used source identification approaches that used local wind observations and air-mass back-trajectory modelling. Local wind observations indicated that the chlorpyrifos measured at Temple Basin was primarily from the Canterbury Plains in New Zealand. Air-mass back-trajectory modelling was not useful when applied at this site.