Organic Contaminants in Agricultural and Alpine Streams in New Zealand

Abstract

Organic contaminants have become widespread in the environment due to the high consumption of materials in the modern lifestyle. The contamination of surface aquatic systems can be particularly crucial because pollutants can pose serious risks to the biological communities residing in these ecosystems. Contaminants can also leach though soil and pollute groundwater resources that are often used as drinking water supply in many parts of the world. Good examples of organic contaminants of concern are pesticides and polycyclic aromatic hydrocarbons (PAHs). In aquatic systems, contaminants can be characterized through different sampling techniques, such as sediment and passive sampling approaches. In the present study, sediment samples were used to investigate the effects of farm management practices on concentrations of halogenated pesticides in streams. The sediment samples were collected from 15 streams arranged in five clusters on the South Island of New Zealand. The streams passed through separate farmlands that were managed using organic, integrated, and conventional practices. The samples were extracted using selective-pressurized liquid extraction (S-PLE) and analysed with a gas chromatograph (GC) coupled with a mass selective detector (MS). The results of the study showed that farm management can negatively affect the pesticide concentrations in streams. Conventional farming was generally associated with higher pesticide concentrations. Organic and integrated farming improved the stream quality, although the streams that passed through these farmlands cannot be considered pesticide-free because the residues of pesticides applied in the past can remain in the environment for a long time. The present study also discusses in detail the principles of aquatic passive sampling, highlighting advantages and disadvantages of the technique. Passive sampling, as opposed to spot measurement approach, provides an integrated record of contaminant concentrations in the environment. This is particularly important for aquatic systems where episodic contamination events are expected to occur. The application of passive samplers normally requires a large quantity of organic solvents to be used in both pre-deployment preparation and analysis steps. In order to minimize the amount of solvent used for the analysis, in the present study a novel method was developed for extracting PAHs from silicon rubber samplers using selective-pressurized liquid extraction (S-PLE), together with post-extraction purification with gel permeation chromatography (GPC). The developed method proved to be satisfactory and the mean recoveries for PAHs using S-PLE and GPC were 75 (%RSD = 20) and 97% (%RSD = 16), respectively. The silicon rubber samplers were used in order to monitor concentration pulses of atmospherically transported PAHs in streams during annual snowmelt. The investigated streams were located in Arthur’s Pass National Park on the South Island of New Zealand. Three sampling sites were chosen; two were located along the Otira River and one along Pegleg Creek River. The passive sampling was conducted in nine consecutive periods from July to December 2010. The samplers were extracted and the resulting extracts were purified using the developed method. All samples were later analysed for PAHs using GC/MS. The results of the analysis showed that PAH water concentrations increased in the study area during the snowmelt period. In addition, the study suggested that weather conditions and sampling site characteristics may have affected the observed PAH concentration patterns at different sites during the study period.