Distribution pattern of PCBs, HCB and PeCB using passive air and soil sampling in Estonia

Passive air sampling survey of the Central and Eastern Europe was initiated in 2006. This paper presents data on toxic organic compounds such as polychlorinated biphenyls (PCB 28, 52, 101, 118, 153, 138, and 180), hexachlorobenzene (HCB), pentachlorobenzene (PeCB), hexachlorocyclohexane compounds (alpha-HCH, beta-HCH,gamma-HCH, delta-HCH), and dichloro-diphenyl-trichloroethane (DDT) compounds (p,p'DDE, p,p'DDD, p,p'DDT, o,p'DDE, o,p'DDD, and o,p'DDT) determined in ambient air and soil samples collected at Estonian monitoring stations.

Ambient air and soil samples were collected in five sites in northern Estonia. Passive air samplers were deployed four times over 4-week periods covering the period April-August 2006. Samples were analyzed using gas chromatography-electron capture detector (HP 5890) supplied with a Quadrex fused silica column 5% Ph for organochlorine pesticides (OCPs). Local ground-boundary wind field was modeled for each monitoring station and sampling period on the basis of observed wind data from the nearest meteorological station with a high quality of time series and compared with upper air (at 850- and 500-hPa level) data from Tallinn-Harku aerological station.

Median levels of PCB at Estonian stations varied between 3 and 9 ng/filter, although the maximum in Kohtla-Järve reached as high as 28 ng/filter. Sampling rates about 3.5 m(3)/day were determined by empirical measurements, making approximately 100 m(3) for a 28-day sampling cycle. In general, OCP levels in soil were at the limit of detection, except Tallinn site and Muuga Port affected mainly by local sources. However, the atmospheric PCB concentrations are in agreement with the soil analyses where highest PCB levels were found in the soil sample for Tallinn (12.0 ng/g dry weight). For HCB, the atmospheric distribution was quite uniform, with the background levels sometimes higher than the urban ones. HCB and PeCB concentrations were very low in May and June when meridional airflow from the southern sector dominated, and concentrations were slightly higher in July and August, most probably due to revolatilization of adsorbed HCB (with PeCB impurities) from former industrial applications during the summer month and possibly enhanced by forest fires in Russia. Also, the highest summary HCH and DDT levels (63.5 and 2.5 ng/filter, respectively) in Estonian monitoring stations were determined at the end of July and beginning of August when the ground-boundary wind direction was from NE with relatively high speed (4-7 m/s). The highest DDT levels in ambient air (3.5 ng/filter) were determined in the spring samples. For DDT and HCH, long-range atmospheric transport clearly dominates persistent OCP, atmospheric input to Estonia as well as for the Scandinavian countries. The DDE/DDT ratio was >1, indicating no fresh input.

The passive air sampling demonstrates uniform distribution of OCPs. In the regional context, there is no indication of increased levels of concentrations of OCPs in the industrial Northeast Estonia where the oil shale processing causes certain pollution impacts. Though the passive sampling does not apply for monitoring of short-term fluxes, the method is capable of reflecting background levels in long-term prospective for potential effect on human health due to long-term exposition of OCPs.

PCB and its congeners, HCB, PeCB, HCH, and DDT were very low in Estonia. None of the persistent organochlorine pesticides have ever been produced in Estonia, and as of today, all old OCP stocks in the country have been destroyed. Highest concentrations could be expected in March and April when southwestern airflow is still strong and dominant, but air humidity is lower and deposition takes place far from the place of origin of OCPs. In summer, the share of locally formed organic compounds increases and deposition depends strongly on weather conditions. In some cases in Tallinn and Muuga where local anthropogenic impact occurs, HCB and PeCB stem from revolatilization of industrial application.

The passive air sampling could be employed more widely to explore long-term human exposure to OCP deposition and assess potential health risks. The survey based on passive air sampling could be extended from Central and Eastern Europe to other European regions to get methodically adjusted cross-European data coverage. Based on the results of the survey, the Lahemaa reference station is a feasible option to represent background monitoring of persistent organic pollutants.