Levels of polycyclic aromatic hydrocarbons in Canadian mountain air and soil are controlled by proximity to roads.

Concentrations of polycyclic aromatic hydrocarbons (PAHs) were measured in soil and XAD-based passive air samples taken from a total of 22 sites along three transects (Revelstoke, Yoho, and Observation, 6-8 sites for each transect) in the mountains of Western Canada in 2003-2004. Median concentrations in air (4-ring PAHs: 33 pg/m(3)) were very low and comparable to those in global background regions such as the Arctic. Low median soil concentrations (16 EPA PAHs: 16 ng/g dry weight) and compositional profiles dominated by naphthalene and phenanthrene are similar to those of tropical soils, indicative of remote regions influenced mostly by PAHs from traffic and small settlements. Comparing levels and composition of PAHs in soils between and along transects indeed suggests a clear relationship with proximity to local sources. Sampling sites that are closer to major traffic arteries and local settlements have higher soil concentrations and a higher relative abundance of heavier PAHs than truly remote sites at higher elevations. This remains the case when the variability in soil organic carbon content between sites is taken into account. Both air/soil concentration ratios and fugacity fractions suggest atmospheric net deposition of four-ring PAHs to soils.

Pesticides in western Canadian mountain air and soil.

The distribution of organochlorine pesticides (OCP; in past and current use) in the mountains of western Canada was determined by sampling air, soil, and lichen along three elevational transects in 2003-2004. Two transects west of the Continental Divide were located in Mount Revelstoke and Yoho National Park, while the Observation Peak transect in Banff National Park is east of the divide. XAD-based passive air samplers, yielding annually averaged air concentrations, were deployed, and soils were collected at all 22 sampling sites, whereas lichen were only sampled in Revelstoke. Back trajectory analysis showed limited air mass transport from the Prairies to the east, but a high frequency of air arriving from the southwest, which includes agricultural regions in British Columbia and Washington State. Endosulfan, dieldrin, and a-hexachlorocyclohexane were the most prevalent OCPs in air and soil; hexachlorobenzene was only abundant in air; chlorothalonil, dacthal, and pentachloronitrobenzene were also consistently present. OCP air concentrations were similar across the three transects, suggesting efficient atmospheric mixing on a local and regional scale. Soil concentrations and soil/air concentration ratios of many OCPs were significantly higher west of the Continental Divide. The soil and lichen concentrations of most OCPs increased with altitude in Revelstoke, and displayed maxima at intermediate elevations at Yoho and Observation Peak. These distribution patterns can be understood as being determined by the balance between atmospheric deposition to, and retention within, the soils. Higher deposition, due to more precipitation falling at lower temperatures, likely occurs west of the divide and at higher elevations. Higher retention, due to higher soil organic matter content, is believed to occur in soils below the tree line. Highest pesticide concentrations are thus found intemperate mountain soils that are rich in organic matter and receive large amounts of cold precipitation.

Accumulation of current-use pesticides in neotropical montane forests.

In Central America, chemical-intensive tropical agriculture takes place in close proximity to highly valued and biologically diverse ecosystems, yet the potential for atmospheric transport of pesticides from plantations to national parks and other reserves is poorly characterized. The specific meteorological conditions of mountain ranges can lead to contaminant convergence at high altitudes, raising particular concern for montane forest ecosystems downwind from pesticide use areas. Here we show, based on a wide-ranging air and soil sampling campaign across Costa Rica, that soils in some neotropical montane forests indeed display much higher concentrations of currently used pesticides than soils elsewhere in the country. Specifically, elevated concentrations of the fungicide chlorothalonil, the herbicide dacthal, and the insecticide metabolite endosulfan sulfate on volcanoes Barva and Poas, lying directly downwind of the extensive banana plantations of the Caribbean lowland, indicate the occurrence of atmospheric transport and wet deposition of pesticides at high altitudes. Calculations with a contaminant fate model, designed for mountain regions and parametrized to the Costa Rican environment, show that chemicals with a log K(AW) between -3 and -5 have a greater potential for accumulation at high altitudes. This enrichment behavior is quantified by the Mountain Contamination Potential and is sensitive to contaminant degradability. The modeling work supports the hypothesis suggested by the field results that it is enhanced precipitation scavenging at high elevations (caused by lower temperatures and governed by K(AW)) that causes pesticides to accumulate in tropical montane areas. By providing for the first time evidence of significant transfer of currently used pesticides to Central American montane cloud forests, this study highlights the need to evaluate the risk that tropical agricultural practices place on the region's ecological reserves.

Organochlorine pesticides in the soils and atmosphere of Costa Rica.

A survey of the contamination of the physical environment of Costa Rica with banned organochlorine pesticides (OCPs) relied on sampling air and soil at 23 stations acrossthe country in 2004. Average annual air concentrations, determined with XAD-based passive samplers, and surface soil concentrations were generally low when compared to values reported for North and Central America, which is consistent with relatively low historical domestic use and little atmospheric inflow from neighboring countries. Statistical analysis and concentration maps reveal three types of spatial distribution: alpha-hexachlorocyclohexane and p,p'-DDD had a relatively uniform distribution across the country; other DDT-related species were greatly elevated over the national average at Manuel Antonio, a National Park on the Pacific coast; and dieldrin, lindane, and chlordane-related species had higher concentrations in Costa Rica's populated Central Valley. An altitudinal transect of stations in the Central Valley shows declining air-soil concentration ratios with elevation for lindane, likely driven by atmospheric inversions and soil organic carbon content. Enantiomeric composition of chiral OCPs in air and soil was close to racemic, with slight depletion of (-)-alpha-HCH, (-)-cis-chlordane, and (+)-trans-chlordane. Estimated air-soil fugacity fractions are highly uncertain but indicate equilibrium conditions for most OCPs, net volatilization of lindane at some sites, and net deposition for p,p'-DDE. The study demonstrates an approach for quickly evaluating the spatial distribution of OCPs in an understudied area, identifying regionally important contaminants and areas of elevated concentrations.

Organic contaminants in mountains.

The study of organic contaminants at high altitudes is motivated by the potential risk that they pose to humans living in, or depending on resources derived from, mountains and to terrestrial and aquatic ecosystems in alpine areas. Mountains are also ideal settings to study contaminant transport and behavior along gradients of climate and surface cover. Information on organic contaminants in mountains is compiled from the literature and synthesized, with a focus on atmospheric transport and deposition, contaminant dynamics in alpine lakes and aquatic organisms, and concentration differences with altitude. Diurnal mountain winds, in connection with enhanced deposition at higher elevations caused by low temperatures and high precipitation rates, conspire to make mid-latitude mountains become convergence zones for selected persistent organic chemicals. In particular, the more volatile constituents of contaminant mixtures seem to become enriched, relative to the less volatile constituents at higher altitudes. For selected contaminants, concentration inversions (i.e., concentrations that increase with elevation) have been observed. A notable difference between cold trapping in high latitudes and high altitudes is the likely importance of precipitation. High rates of snow deposition in mid- and high-latitude mountains may lead to a large contaminant release during snowmelt. Regions above the tree line often have little capacity to retain the released contaminants, suggesting the potential for a highly dynamic contaminant fate situation during the snow-free season with significant revolatilization and runoff. The chemical and environmental factors that control the orographic cold trapping of organic contaminants should be examined further by measuring and comparatively interpreting concentration gradients along several mountain slopes with widely different characteristics. Future efforts should further focus on the bioaccumulation and potential effects of contaminants in the upper trophic levels of alpine food chains, on measuring more water-soluble, persistent organic contaminants, and on studying how climate change may affect contaminant dynamics in mountain settings.

Simulating the influence of snow on the fate of organic compounds.

Snow scavenging, a seasonal snowpack, and a dynamic water balance are incorporated in a non-steady-state generic multimedia fate model in order to investigate the effect of snow on the magnitude and temporal variability of organic contaminant concentrations in various environmental media. Efficient scavenging of large nonpolar organic vapors and particle-bound organic chemicals by snow can lead to reduced wintertime air concentrations and incorporation in the snowpack. The snow cover functions as a temporary storage reservoir that releases contaminants accumulating over the winter during a short melt period, resulting in temporarily elevated concentrations in air, water, and soil. The intensity of these peaks increases with the length of the snow accumulation period. Organic chemicals of sufficient volatility (log KOA < 9; e.g., light polychlorinated biphenyls) can volatilize from the snowpack, resulting in springtime concentration maxima in the atmosphere. The behavior of fairly water-soluble chemicals during snowmelt depends on their relative affinity for the newly formed liquid water phase and the rapidly diminishing ice surface-quantitatively expressed by their interface-water partition coefficient (KIW). Chemicals with a preference for the dissolved phase (low KIW; e.g., pentachlorophenol) can become enriched in the first meltwater fractions and experience a temporary concentration peak in lakes and rivers. Organic chemicals that are neither volatile enough to evaporate from the snowpack nor sufficiently water soluble to dissolve in the meltwater (e.g., polybrominated diphenyl ethers) sorb to the particles in the snowpack. These particles may be sufficiently contaminated to constitute the major input route to the terrestrial environment upon release during snowmelt. Because wintertime deposition to the snowpack may be higher than to a non-snow covered surface, this can result in higher soil concentrations of persistent organic contaminants in the long term. The potential ecotoxicological significance of peak exposures demands a better understanding of the role of snow in the fate of organic contaminants.