Bondi Gevao

Bound pesticide residues in soils: a review.

This article is a review of the current state of knowledge regarding the formation and biological/environmental significance of bound pesticide residues in soils. We begin by defining various terms used in our discussions and identifying the types/classes of pesticides which may be added to soil and interact with it. We then consider various soil properties and aspects of land management which will influence the nature and degree of the soil-pesticide association and discuss the possible physical and chemical binding mechanisms. We then move on to consider the role of microorganisms and other forms of soil biota in bound residue formation and the bioavailability of soil-borne pesticide residues. The review ends with a consideration of the significance of bound pesticide residues.

Measuring and modelling the vertical distribution of semi-volatile organic compounds in soils. I : PCB and PAH soil core data

Soil cores were collected from undisturbed soils at four locations in the UK and analysed for PCBs, PAHs and soil organic carbon. In all four soil cores ΣPCB and ΣPAH concentrations peaked at or just below the soil surface and declined with depth. Statistically significant correlations were obtained between compound concentrations and organic carbon content in all four soil cores. PAH and PCB homologue profiles at different soil depths and horizons provided information on transport of the compounds in the soils. Fairly constant homologue profiles with depth in the cores suggested that bioturbation may be an important soil transport process for PCBs and PAHs.

Polychlorinated biphenyl and polycyclic aromatic hydrocarbon deposition to and exchange at the air–water interface of Esthwaite Water, a small lake in Cumbria, UK

Atmospheric concentrations and deposition fluxes of several polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were measured concurrently over a 1-year period at a shore-based site at Esthwaite Water, to estimate their loadings from the atmosphere to the lake water surface. The PAH deposition fluxes (μg m−2 month−1) to conventional upturned Frisbees varied from 0.19 (anthracene) to 7.8 (phenanthrene), with a ΣPAH deposition of 33.5. Phenanthrene, fluoranthene and pyrene contributed >50% of the ΣPAH deposited. The deposition fluxes of PCBs ranged from 0.03 (octa-PCBs) to 0.38 (tri-PCBs) μg m−2 month−1 with a ΣPCB flux estimated at 0.87 μg m−2 month−1. The coefficients of variation of deposition varied from 75% (octa-PCBs) to 120% (tri-PCBs) and from 90 to 150% for individual PAHs. Temporal variability in fluxes to the collector was large, suggesting highly variable atmospheric concentrations and scavenging processes. Atmospheric PAH concentrations were negatively correlated with temperature over the sampling period, suggesting that the source function—rather than temperature-dependent, air–surface equilibrium partitioning—primarily controlled air concentrations. Deposition fluxes of PAHs correlated well with rainfall between January and September, suggesting that particle washout was the main factor controlling deposition over this period. The controlling factor for deposition between October and December was related to the increased source function of the compounds to the atmosphere. Regression analysis of the data for PAHs with ≥4 rings gave a strong positive correlation between the deposition flux and atmospheric concentrations, suggesting that the transfer of compounds occurred with a similar efficiency. Simultaneous air and water sampling over an annual cycle was used to calculate fugacity quotients for individual PAHs and PCBs. These calculations showed that PCBs were outgassing from the lake water throughout the year (i.e. volatilisation>deposition) whilst PAH transfers varied seasonally with net deposition in winter months when there is no ice cover, and net volatilisation at all other times.

Temperature dependence of PCBs in the UK atmosphere.

A thermodynamic approach was taken to assess the state of equilibrium between air and the Earth’s surface for PCBs at a variety of sites located in urban and rural areas. The Clausius–Clapeyron equation was applied to atmospheric PCB data, relating PCB partial vapour pressure (ln P) to inverse temperature (1/K); essentially representing the temperature controlled transition between condensed phases and the atmospheric gas phase. The slopes of the resulting plots ranged from −3100 to −8272 for a range of congeners at two city sites, significantly steeper than those generated at two rural locations, where there was little or no correlation between ln P and temperature. It was inferred that advection and variable meteorological conditions mask any localised, temperature dependent, air–surface exchange at these rural locations when weekly or two weekly integrated samples were taken. At a third rural site, close to Lancaster University, an intensive highly time-resolved sampling regime, carried out during very stable meteorological conditions resulted in highly correlated plots (r2>0.6), with slopes ranging from −7151 to −14 148 for different congeners. By reducing meteorological variables in this manner localised temperature controlled air–surface exchange became evident. Enthalpies of phase change generated from the temperature coefficients were similar to literature values for the enthalpy of vapourisation and the enthalpy of phase change from octanol to air. This suggests that, under these stable conditions, equilibrium was achieved as a function of either vapour pressure (P°L) or the octanol–air partition coefficient (KOA).

Polycyclic aromatic hydrocarbon (PAH) deposition to and processing in a small rural lake, Cumbria UK

Abstract PAH concentrations were determined in a dated sediment core collected from Esthwaite Water (EW), a seasonally anoxic lake in the English Lake District. The most dramatic variations are associated with increased PAH fluxes from ∼1900 and a sub-surface maximum (∼29 mg m−2 year−1) in the late 1960s to early 1970s, followed by a fivefold decrease in fluxes to the sediment-water interface. This trend is believed to reflect enhanced fossil fuel burning, followed by general improvements in combustion technologies, shifts in the fuels used for domestic space heating and the implementation of various emission controls on releases from certain known PAH sources. When the relative contributions from individual compounds to the ∑PAH were plotted as vertical profiles, coherent time trends emerged. Perylene dominated the pre-1900 sedimentary PAH composition, contributing >75% to the ∑PAH mixture. The perylene profile provides good evidence for both natural and anthropogenic sources to EW. The ratios of annual sediment trap fluxes to surficial sediment accumulation rates are substantially greater than one for the low molecular weight compounds, suggesting release at or near the sediment water interface and subsequent recycling of these compounds. Recycling was found to increase with increasing solubility and decreasing log Kow.

Diurnal fluctuations in polybrominated diphenyl ether concentrations during and after a severe dust storm episode in Kuwait City, Kuwait.

Concentrations of polybrominated diphenyl ethers (PBDEs) were quantified in four-hour integrated air samples obtained serially over a five day period in May 2007 in Kuwait City during and after a severe dust storm. The ∑PBDE concentrations ranged from 51 to 1307 pg m(-3) for the first two days of sampling and 20 to 148 pg m(-3) for the rest of the sampling period. The first two days of sampling occurred during a severe dust storm episode when the total suspended particulates (TSP) in air exceeded 1000 μg/m(3) with concentrations peaking during the day and decreasing at night. During this dust episode, the peak nighttime PBDE concentration was 30 times higher than the minimum daytime concentration. Although ∑PBDE concentrations peaked at night during the first two sampling days, the fluctuations in the BDE 47:99 ratio tracked changes in ambient temperature remarkably well, following a clear diurnal pattern. The fraction of congeners in the gas phase varied inversely with solar flux and was lower on days with a high number of hours of sunshine, suggesting that photolytic degradation of gas-phase PBDEs was occurring.