Hexachlorocyclohexanes in the Canadian archipelago. 1. Spatial distribution and pathways of alpha-, beta- and gamma-HCHS in surface water.

Hexachlorocyclohexanes (HCHs) in the surface water of the Canadian Archipelago and south Beaufort Sea were measured in summer, 1999. Overall concentrations of HCH isomers were in order of abundance: alpha-HCH (3.5 +/- 1.2 ng L(-1)) > gamma-HCH (0.31 +/- 0.07 ng L(-1)) > beta-HCH (0.10 +/- 0.03 ng L(-1)). Concentrations and ratios of alpha-HCH/gamma-HCH decreased significantly (p < 0.001 to 0.003) from west to east, but there was no significant variation in alpha-HCH/ beta-HCH. The (+) enantiomer of alpha-HCH was preferentially degraded, with enantiomer fractions (EFs) ranging from 0.432-0.463 and increasing significantly (p < 0.001) from west to east. Concentrations also varied latitudinally for alpha-HCH and gamma-HCH (p < 0.002) but not for beta-HCH. Principal component analysis with variables alpha-HCH and gamma-HCH concentrations, EF, latitude, and longitude accounted for 71% (PC 1) and 16% (PC 2) of the variance. Mixing in the eastern Archipelago was modeled by assuming three end members with characteristic concentrations of alpha-HCH and gamma-HCH. The model accounted for the observed concentrations and higher EFs of alpha-HCH at the eastern stations.

Modelling of the long-term fate of pesticide residues in agricultural soils and their surface exchange with the atmosphere: Part II. Projected long-term fate of pesticide residues.

In the first part of this paper, a simple coupled dynamic soil-atmosphere model for studying the gaseous exchange of pesticide soil residues with the atmosphere is described and evaluated by comparing model results with published measurements of pesticide concentrations in air and soil. In Part II, the model is used to study the concentration profiles of pesticide residues in both undisturbed and annually tilled agricultural soils. Future trends are estimated for the measured air and soil concentrations of lindane and six highly persistent pesticides (toxaphene, p,p'-DDE, dieldrin, cis- and trans-chlordane and trans-nonachlor) over a twenty-year period due to volatilization and leaching into the deeper soil. Wet deposition and particle associated pesticide deposition (that increase soil residue concentrations) and soil erosion, degradation in the soil (other than for lindane) and run-off in precipitation are not considered in this study. Estimates of the rain deposition fluxes are reported that show that, other than for lindane, net volatilization fluxes greatly exceed rain deposition fluxes. The model shows that the persistent pesticides studied are highly immobile in soil and that loss of these highly persistent residues from the soil is by volatilization rather than leaching into the deeper soil. The soil residue levels of these six pesticides are currently sources of net volatilization to the atmosphere and will remain so for many years. The maximum rate of volatilization from the soil was simulated by setting the atmospheric background concentration to zero; these simulations show that the rates of volatilization will not be significantly increased since soil resistance rather than the atmospheric concentration controls the volatilization rates. Annual tilling of the soils increases the volatilization loss to the atmosphere. Nonetheless, the model predicts that, if only air-soil exchange is considered, more than 76% of current persistent pesticide residues will remain after 20 years in the top 7 cm of annually tilled soils. In contrast, lindane is relatively mobile in soil due to weaker binding to soil carbon and leaching of lindane into soil is the main removal route for current lindane residues near the soil surface. The model predicts that the soil is a sink for lindane in the atmosphere and that soil residue levels of lindane in the surface soil are determined by a balance between dry gaseous deposition to the soil from the atmosphere and leaching from the surface soil into the deeper soil where degradation is the dominant loss route. The model suggests that deposition of lindane from the atmosphere will sustain residues in the soil and, in the absence of fresh applications of lindane to the soil, eliminating lindane from the atmosphere would lead to a rapid decline of lindane residues in agricultural soils of the southern U.S.

Modelling of the long term fate of pesticide residues in agricultural soils and their surface exchange with the atmosphere: Part I. Model description and evaluation.

Sources of pesticides in the atmosphere can be releases of new material through current use, or emission/reemission from soil residues resulting from historical use. It is the latter aspect, soil residues, that is the focus of this study. This paper describes the application of a simple coupled atmosphere-soil pesticide exchange model that can assist in the interpretation of soil residue and air concentration measurements, and in the projection of short period field measurements to larger spatial scales and longer time periods. Only dry gaseous exchange (emission and deposition) between bare agricultural lands and the atmosphere is modelled. Wet deposition and particle associated deposition of pesticide are not included. Model results are compared with published co-located air and soil pesticide concentration measurements made on agricultural lands in the southern U.S. that have soil residues of lindane and the following six highly persistent pesticides: cis-, trans-chlordane, p,p'-DDE, dieldrin, trans-nonachlor and toxaphene. The study results show: (i) that measured air concentrations of toxaphene and p,p'-DDE above agricultural soils in the southern U.S. can be attributed to emissions due to local soil residues of these pesticides rather than to the regional background air concentrations; (ii) that both soil emissions and background air concentrations of dieldrin contribute significantly to the measured air concentrations; (iii) that measured air concentrations of cis- and trans-chlordane as well as trans-nonachlor and lindane are mainly due to the regional background with little contribution from local soil residues. An analysis of modelled summer day and night average soil-air exchange fluxes shows that toxaphene and p,p'-DDE soil residues are strong sources of emission to the atmosphere during both the day and night while the chlordanes, trans-nonachlor, lindane and dieldrin are deposited from the atmosphere to the soil during the night hours and emitted to the atmosphere during the day time. This result illustrates the model's capability to simulate the processes that lead to the 'grasshopper' effect whereby persistent pesticides in soils can be transported in the atmosphere by successive periods of emission and deposition to terrestrial surfaces. In the second part to this paper, the model is used to study the trends of pesticide residues and air concentrations over a twenty year period.

Temporal and spatial variabilities of atmospheric polychlorinated biphenyls (PCBs), organochlorine (OC) pesticides and polycyclic aromatic hydrocarbons (PAHs) in the Canadian Arctic: results from a decade of monitoring.

The Northern Contaminants Program (NCP) baseline monitoring project was established in 1992 to monitor for persistent organic pollutants (POPs) in Arctic air. Under this project, weekly samples of air were collected at four Canadian and two Russian arctic sites, namely Alert, Nunavut; Tagish, Yukon; Little Fox Lake, Yukon; Kinngait, Nunavut; Dunai Island, Russia and Amderma, Russia. Selected POPs, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine (OC) pesticides, were analyzed in both the gas and particulate phases. This paper summarizes results obtained from this project in the past 5 years. Temporal trends were developed for atmospheric PCBs and OCs observed at Alert using a digital filtration (DF) technique. It was found that trends developed with 5 years of data (1993-1997) did not differ significantly from those determined with 7 years of data (1993-1999). This implies that with the DF technique, long-term trends can still be developed with less than 10 years of data. An acceleration in decline of OC and PCB air concentrations was noted in 1999 for some compounds, although the reason is unknown. Monitoring efforts must continue to assess the effect of this decline on the long-term trends of POPs in the Canadian Arctic. Occasional high trans-/cis-chlordane ratios and heptachlor air concentrations measured at Alert between 1995 and 1997 suggests sporadic fresh usage of chlordane-based pesticides. However, significant decreasing trends of chlordanes along with their chemical signatures has provided evidence that emission of old soil residues is replacing new usage as an important source to the atmosphere. Measurements of OC air concentrations conducted at Kinngait in 1994-1995 and 2000-2001 indicated faster OC removal at this location than at Alert. This may be attributed to the proximity of Kinngait to temperate regions where both biotic and abiotic degradation rates are faster. The PAH concentrations observed at Alert mimic those at mid-latitudes and are consistent with long-range transport to the Arctic, particularly for the lighter PAHs. A decline in particulate PAH was observed, similar to atmospheric sulphate aerosol and can be attributed to the collapse of industrial activity in the former Soviet Union between 1991 and 1995. Spatial comparisons of OC seasonality at Alert, Tagish, Dunai and Kinngait show elevated air concentrations of some compounds in spring. However, elevated spring concentrations were observed for different compounds at different sites. Potential causes are discussed. Further investigation in the atmospheric flow pattern in spring which is responsible for the transport of POPs into the Arctic is required. OC and PCB air concentrations at Alert were found to be influenced by two climate variation patterns, the North Atlantic Oscillation (NAO) and the Pacific North American (PNA) pattern. Planetary atmospheric patterns must be taken into account in the global prediction and modelling of POPs in the future.

Modern and historical fluxes of halogenated organic contaminants to a lake in the Canadian arctic, as determined from annually laminated sediment cores.

Two annually laminated cores collected from Lake DV09 on Devon Island in May 1999 were dated using 210Pb and 137Cs, and analyzed for a variety of halogenated organic contaminants (HOCs), including polychlorinated biphenyls (PCBs), organochlorine pesticides, short-chain polychlorinated n-alkanes (sPCAs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polybrominated diphenyl ethers (PBDEs). Dry weight HOC concentrations in Lake DV09 sediments were generally similar to other remote Arctic lakes. Maximum HOC fluxes often agreed well with production maxima, although many compound groups exhibited maxima at or near the sediment surface, much later than peak production. The lower than expected HOC concentrations in older sediment slices may be due to anaerobic degradation and possibly to dilution resulting from a temporary increase in sedimentation rate observed between the mid-1960s and 1970s. Indeed, temporal trends were more readily apparent for those compound classes when anaerobic metabolites were also analyzed, such as for DDT and toxaphene. However, it is postulated here for the first time that the maximum or increasing HOC surface fluxes observed for many of the major compound classes in DV09 sediments may be influenced by climate variation and the resulting increase in algal primary productivity which could drive an increasing rate of HOC scavenging from the water column. Both the fraction (F(TC)) and enantiomer fraction (EF) of trans-chlordane (TC) decreased significantly between 1957 and 1997, suggesting that recent inputs to the lake are from weathered chlordane sources. PCDD/Fs showed a change in sources from pentachlorophenol (PeCP) in the 1950s and 1960s to combustion sources into the 1990s. Improvements in combustion technology may be responsible for the reducing the proportion of TCDF relative to OCDD in the most recent slice.

The transport of beta-hexachlorocyclohexane to the western Arctic Ocean: a contrast to alpha-HCH.

A large database for alpha-hexachlorocyclohexane (alpha-HCH), together with multimedia models, shows this chemical to have exhibited classical 'cold condensation' behavior. The surface water of the Arctic Ocean became loaded between 1950 and 1990 because atmospheric transport of alpha-HCH from source regions to the Arctic was rapid and because alpha-HCH partitioned strongly into cold water there. Following emission reductions during the 1980s, alpha-HCH remained trapped under the permanent ice pack, with the result that the highest oceanic concentrations in the early 1990s were to be found in surface waters of the Canada Basin. Despite a much stronger partitioning into water than for alpha-HCH, beta-HCH did not accumulate under the pack ice of the Arctic Ocean, as might be expected from the similar emission histories for the two chemicals. Beta-HCH appears to have loaded only weakly into the high Arctic through the atmosphere because it was rained out or partitioned into North Pacific surface water. However, beta-HCH has subsequently entered the western Arctic in ocean currents passing through Bering Strait. Beta-HCH provides an important lesson that environmental pathways must be comprehensively understood before attempting to predict the behavior of one chemical by extrapolation from a seemingly similar chemical.

Chiral analysis of organochlorine pesticides in Alabama soils.

The enantiomeric composition of organochlorine (OC) pesticide residues was investigated in 32 agricultural and 3 cemetery soils from Alabama. The enantiomeric signatures were similar to those from other soils in US and Canada. The enantiomer fractions (EFs) of o,p'-DDT showed great variability, ranging from 0.41 to 0.57 while the EFs of chlordanes and chlordane metabolites were less variable and differed in general significantly from racemic. Enantioselective depletion of (+)trans-chlordane, (-)cis-chlordane, the first eluting enantiomer of MC5, and enrichment of (+)heptachlor-exo-epoxide and (+)oxychlordane was found in a large majority of the samples with detectable residues. The enantiomeric composition of alpha-hexachlorocyclohexane was racemic or close to racemic.

Soil-air exchange model of persistent pesticides in the United States cotton belt.

Measurements of organochlorine pesticides (lindane, cis-chlordane [CC], trans-chlordane [TC], trans-nonachlor [TN]), dieldrin, p,p'-dichlorodiphenyldichloroethylene [DDE], and toxaphene) in Alabama, USA, air and soil were used to assess the soil-air equilibrium status and to identify compounds with significant contributions to observed air burdens. Of the compounds tested, p,p'-DDE and toxaphene showed a significant potential for outgasing, followed by dieldrin and trans-nonachlor, which showed moderate outgasing potentials. Lindane, cis-chlordane, and trans-chlordane were near soil-air equilibrium. A fugacity-based, multilayered soil-air exchange model was used to predict temporal trends of chemical in air and soil resulting from reemission of soil residues to a presumed clean atmosphere (maximum emission scenario). Results showed that p,p'-DDE and toxaphene accounted for up to 50% of the observed air burden and that approximately 200 to 600 kg of p,p'-DDE and 3,000 to 11,000 kg to toxaphene are released to the atmosphere each year by soils in Alabama (area = 1.23 x 10(11) m2). High annual net fluxes were also predicted for dieldrin and trans-nonachlor (300-1,100 kg and 150-500 kg, respectively), but these only account for up to approximately 20% of their observed air burdens.

Concentrations and fluxes of hexachlorocyclohexanes and chiral composition of alpha-HCH in environmental samples from the southern Baltic Sea.

In summer 1997 and winter 1998, paired boundary air and surface water samples were collected during cruises in the southern Baltic Sea. Simultaneously, deposition samples were taken at Gotland Island, located close to the air-water sampling area. Water samples taken shortly after the flooding of Oder and Wisla Rivers in summer 1997 were also included in the study. Concentrations and gas exchange fluxes of alpha- and gamma-HCH and chiral composition of alpha-HCH were determined. According to fugacity calculations, the HCHs were close to air-sea partitioning equilibrium. The net fluxes varied over time, particularly during summer. Importance of the air to sea removal routes "gross gas deposition" and "wet deposition" were about equal for gamma-HCH, while the scavenging via precipitation was less important for alpha-HCH. Enantiomer fractions were used to estimate the fraction of alpha-HCH in the boundary air layer that had volatilized from the water. During summer, the fraction was approximately 60%, and wintertime significantly less (0-35%). Variations in air mass origin were clearly reflected in net air-sea gas exchange and isomeric and enantiomeric "signatures" in boundary air. The composition of boundary air and precipitation was also variable depending on season.

Contaminants in the Canadian Arctic: 5 years of progress in understanding sources, occurrence and pathways.

Recent studies of contaminants under the Canadian Northern Contaminants Program (NCP) have substantially enhanced our understanding of the pathways by which contaminants enter Canada's Arctic and move through terrestrial and marine ecosystems there. Building on a previous review (Barrie et al., Arctic contaminants: sources, occurrence and pathways. Sci Total Environ 1992:1-74), we highlight new knowledge developed under the NCP on the sources, occurrence and pathways of contaminants (organochlorines, Hg, Pb and Cd, PAHs, artificial radionuclides). Starting from the global scale, we examine emission histories and sources for selected contaminants focussing especially on the organochlorines. Physical and chemical properties, transport processes in the environment (e.g. winds, currents, partitioning), and models are then used to identify, understand and illustrate the connection between the contaminant sources in industrial and agricultural regions to the south and the eventual arrival of contaminants in remote regions of the Arctic. Within the Arctic, we examine how contaminants impinge on marine and terrestrial pathways and how they are subsequently either removed to sinks or remain where they can enter the biosphere. As a way to focus this synthesis on key concerns of northern residents, a number of special topics are examined including: a mass balance for HCH and toxaphene (CHBs) in the Arctic Ocean; a comparison of PCB sources within Canada's Arctic (Dew Line Sites) with PCBs imported through long-range transport; an evaluation of concerns posed by three priority metals--Hg, Pb and Cd; an evaluation of the risks from artificial radionuclides in the ocean; a review of what is known about new-generation pesticides that are replacing the organochlorines; and a comparison of natural vs. anthropogenic sources of PAH in the Arctic. The research and syntheses provide compelling evidence for close connectivity between the global emission of contaminants from industrial and agricultural activities and the Arctic. For semi-volatile compounds that partition strongly into cold water (e.g. HCH) we have seen an inevitable loading of Arctic aquatic reservoirs. Drastic HCH emission reductions have been rapidly followed by reduced atmospheric burdens with the result that the major reservoir and transport agent has become the ocean. In the Arctic, it will take decades for the upper ocean to clear itself of HCH. For compounds that partition strongly onto particles, and for which the soil reservoir is most important (e.g. PCBs), we have seen a delay in their arrival in the Arctic and some fractionation toward more volatile compounds (e.g. lower-chlorinated PCBs). Despite banning the production of PCB in the 1970s, and despite decreases of PCBs in environmental compartments in temperate regions, the Arctic presently shows little evidence of reduced PCB loadings. We anticipate a delay in PCB reductions in the Arctic and environmental lifetimes measured in decades. Although artificial radionuclides have caused great concern due to their direct disposal on Russian Shelves, they are found to pose little threat to Canadian waters and, indeed, much of the radionuclide inventory can be explained as remnant global fallout, which was sharply curtailed in the 1960s, and waste emissions released under license by the European reprocessing plants. Although Cd poses a human dietary concern both for terrestrial and marine mammals, we find little evidence that Cd in marine systems has been impacted by human activities. There is evidence of contaminant Pb in the Arctic, but loadings appear presently to be decreasing due to source controls (e.g. removal of Pb from gasoline) in Europe and North America. Of the metals, Hg provokes the greatest concern; loadings appear to be increasing in the Arctic due to global human activities, but such loadings are not evenly distributed nor are the pathways by which they enter and move within the Arctic well understood.

Polycyclic aromatic hydrocarbons in storm runoff from urban and coastal South Carolina.

Stormwater runoff was collected in urbanized areas of South Carolina to investigate the levels and sources of polycyclic aromatic hydrocarbons (PAHs). Mean concentrations of total PAHs in runoff (sum(PAHs), 14 compounds), determined by gas chromatography-mass spectrometry, were 5590 ng/l in the city of Columbia and 282 ng/l in the coastal community of Murrells Inlet. Lower concentrations were found in estuarine water at Murrells Inlet (mean = 35 ng/l) and at undeveloped North Inlet estuary (13 ng/l). The PAH profiles in Columbia and Murrells Inlet runoff were similar to those of atmospheric particulate matter and unlike those in used crankcase oil. Examination of the aliphatic fraction of Columbia runoff samples by gas chromatography with flame ionization detection showed patterns that were more similar to used crankcase oil than to urban aerosols.

Residues of organochlorine pesticides in Alabama soils.

A survey was made of 36 Alabama agricultural soils to assess residues of formerly used organochlorine pesticides. Compounds determined comprised alpha- and gamma-hexachlorocyclohexane, heptachlor, heptachlor-exo-epoxide, trans- and cis-chlordane, trans-nonachlor, dieldrin, toxaphene, DDT and DDE. Concentrations varied by several orders of magnitude among farms and appeared to be log-normally distributed. Highest concentrations (ng g(-1) dry soil, arithmetic means) were found for toxaphene (285+/-390) and DDTs (p,p'-DDE, 22.7+/-21.4; p,p'-DDT, 24.6+/-30.5; o,p'-DDT, 4.00+/-5.86; p,p'-DDD, 2.40+/-2.41) which were once heavily used in the southern USA. Pesticide residues were not proportional to soil organic carbon content indicating that residue concentrations were a reflection of pesticide application history and dissipation rates rather than air-soil equilibrium. Mean ratios of DDT/DDE in six regions of the state ranged from 0.39 to 1.5, and compound ratios for chlordanes and toxaphene were different from those in the technical mixtures.

Peer reviewed: using enantiomers to trace pesticide emissions.

This novel approach provides clues to sources of pesticides found in the atmosphere.

Organochlorine pesticides and enantiomers of chiral pesticides in Arctic Ocean water.

In the summers of 1993 and 1994, seawater samples from the surface layer (40-60 m) were collected to determine the spatial distribution of organochlorine pesticides on expeditions that crossed the Arctic Ocean from the Bering and Chukchi seas to the North Pole, to a station north of Spitsbergen, and then south into the Greenland Sea. Spatial differences in concentration were found that varied with the pesticide. Heptachlor exo-epoxide (a metabolite of heptachlor) and alpha-hexachlorocyclohexane (alpha-HCH) increased from the Chukchi Sea to the pole, and then decreased toward Spitsbergen and Greenland Sea. Chlorinated bornanes (toxaphene) followed a similar trend, but levels were also high near Spitsbergen and in the Greenland Sea. A reverse trend was found for endosulfan, with lower concentrations in the ice-covered regions. Little variation was seen in chlordane concentrations, although the ratio of trans-/cis-chlordane decreased at high latitudes. Several of these pesticides are chiral: alpha-HCH, cis- and trans-chlordane, and heptachlor exo-epoxide. Enantioselective degradation of (-)alpha-HCH was found in the Bering and Chukchi seas, whereas the (+)enantiomer was depleted in the Arctic Ocean and Greenland Sea. Enrichment of (+)heptachlor exo-epoxide was found in all regions. Trans- and cis-chlordane were nearly racemic.

Air-water gas exchange and evidence for metabolism of hexachlorocyclohexanes in Resolute Bay, N.W.T.

Paired air and water samples were collected at Resolute Bay (74 degrees N, 95 degrees W) in summer 1992 to estimate the direction of gas exchange of hexachlorocyclohexanes (HCHs) and investigate possible loss processes in the water column. Average concentrations of alpha-HCH and gamma-HCH in ocean surface water were 4.7 +/- 0.9 and 0.44 +/- 0.11 ng/l, respectively. These alpha- and gamma-HCH levels are approximately 66-104% and 54-72% of values reported for the central Arctic Ocean at the Canadian Ice Island in 1986. Mean atmospheric concentrations of alpha-HCH and gamma-HCH (114 +/- 16 and 9.8 +/- 1.3 pg/m3) were 2-3 times lower than summer Arctic levels in the 1980s. The ocean surface water (-1.4 degrees C) was approximately within Henry's Law equilibrium with respect to atmospheric gamma-HCH levels. Water/air fugacity ratios were 1.03 for gamma-HCH and 1.57 for alpha-HCH, indicating a slight potential for volatilization of alpha-HCH. The two alpha-HCH enantiomers in air and water were separated by chromatography on a gamma-cyclodextrin capillary column. The enantiomeric ratio (ER = ratio of (+)alpha-HCH/(-)alpha-HCH) in air was 1.00 +/- 0.04. This agrees excellently with ER = 1.00 +/- 0.01 found for a racemic alpha-HCH standard. The (+) enantiomer was depleted in seawater, resulting in ER = 0.93 +/- 0.06 in Resolute Bay. ERs of samples from Amituk Lake on Cornwallis Island ranged from 0.65 to 0.99, depending on location, date and relative contributions of fresh snowmelt and older lake water. These results suggest that microbial degradation of HCHs is taking place in Arctic lakes and near-shore marine waters.