Environ. Sci. Technol. 2001, 35, 1989-1995
Organochlorine Pesticide Residues in Archived UK Soil S . N . M E I J E R , * ,§ C . J . H A L S A L L , § T. HARNER,# A. J. PETERS,‡ W. A. OCKENDEN,§ A. E. JOHNSTON,† AND K. C. JONES§ Environmental Science Department, Institute of Environmental and Natural Sciences, Lancaster University, Lancaster, LA1 4YQ, UK, Meteorological Service of Canada, Environment Canada, 4905 Dufferin Street, Downsview, Ontario M3H 5T4, Canada, Centre for Ecology and Hydrology, Natural Environment Research Council, Winfrith Technology Centre, Dorchester, Dorset DT2 8ZD, UK, and Rothamsted Experimental Station, Harpenden, Hertfordshire AL5 2JQ, UK
Archived background soils (“Broadbalk’, 1944-1986) and sludge-amended soils (“Luddington”, 1968-1990), collected from long-term agricultural experiments in the UK, were analyzed for a range of organochlorine (OC) pesticides to establish trends over time. Concentrations typically ranged from 0.1 to 10 ng/g of soil (dry weight), with γ-hexachlorocyclohexane (γ-HCH), dieldrin, and p,p′-DDE consistently having the highest concentrations. The trends in the Broadbalk background soils are largely consistent with usage patterns, with peak concentrations occurring in the 1960s for DDTs and between the 1960s and the 1980s for the other OCs. In the Luddington control and sludge-amended soils, several of the OCs show a significant decline in concentrations from the late 1960s to 1990, with half-lives ranging from ∼7 years (R-HCH) to ∼25 years (dieldrin). The sludge-amended plot received 125 tonnes of sludge per ha in 1968, which was mixed in to a depth of 15 cm. It appears that the sludge treatment had little effect on concentrations in the soil, with no significant difference between control soil and sludge-amended soil for most compounds, except for HCB, p,p′-DDE, and dieldrin. Enantiomeric fractions (EFs) of some chiral pesticides (R-HCH, cis- and trans-chlordane, and o,p′-DDT) were determined in the Luddington soils. Results reveal that enantioselective degradation of OC pesticides is occurring in these soils for trans-chlordane (TC) and cis-chlordane (CC). However, the depletion over time is not statistically significant, and there is no statistically significant difference between EFs in the control soil and sludge-amended soil. This indicates that enantioselective microbial degradation was not consistent over time and that the addition of sludge to soil did not significantly alter the enantiomeric preference of the microbial community.
Introduction Many organochlorine pesticides (OCs) are semivolatile and lipophilic and fall into the class of compounds described as * Corresponding author phone: +44 1524 592578; fax: +44 1524 593985; e-mail:
[email protected]. † Rothamsted Experimental Station. ‡ Winfrith Technology Centre. § Lancaster University. # Meteorological Service of Canada, Environment Canada. 10.1021/es0000955 CCC: $20.00 Published on Web 04/20/2001
2001 American Chemical Society
persistent organic pollutants (POPs). In industrialized western countries their use has been restricted or even banned for several years. However, because of their long environmental residence times, these compounds are still found in sediments, soils, and air. Several of these compounds including p,p′-DDT, chlordanes, and dieldrin are included in the recent United Nations Economic Commission for Europe (UN-ECE) 1998 Convention on Long-range Transboundary Air Pollution (CLTAP) protocol on POPs, which proposes a list of 16 substances that have been identified according to agreed risk criteria. The ultimate objective of the protocol is to eliminate any discharges and emissions of these substances (1). There is therefore considerable interest in how environmental levels will respond to source and use reduction measures. In the UK there is limited information regarding historical usage of OC pesticides and contemporary residues in soils and sediments. In this study we used a unique archive of soils from long-term experiments in the UK to investigate the persistence of a range of OC pesticides. Some of these soils, collected from agricultural plots at the Rothamsted Experimental Station (RES) in the south of England, have been used previously to examine the time series of other POPs such as polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) (2, 3). The focus of the study was on changes in background concentrations, because the soils did not have any direct applications of pesticides. Residues therefore reflected the net effect of atmospheric deposition (and sludge-amendment) inputs and volatilization, biodegradation, and other losses. Evidence from studies on ambient UK air indicates that volatilization from soil plays a key role in controlling the occurrence of R- and γ-hexachlorocyclohexane (R- and γ-HCH), dieldrin, p,p′-DDE, and hexachlorobenzene (HCB) in contemporary air at several rural sites (4, 5). Specifically, the purpose of this study was 3-fold. First, to establish a time series of background soil concentrations. This was achieved using “control” (untreated) soils from the Broadbalk Classical Experiment at Rothamsted (6) sampled from the mid-1940s to the early 1990s, effectively covering the period when OC pesticide use was at its peak. Second, to examine the effects of sewage sludge addition on concentrations of OC pesticides and their rates of decline in the soil. This used soils from the Luddington experiment, which received a large application (125 t ha-1) of sewage sludge in 1968 (7). Third, the Luddington samples were subjected to chiral analysis of selected pesticides. Chiral pesticides are manufactured as racemic mixtures, containing equal amounts of the two enantiomers. These enantiomers can be broken down enantioselectively by microorganisms in various environments, yielding nonracemic residues that can be differentiated from “fresh” pesticides. Enantiomer profiles of chiral pesticides in soil, water, and air are increasingly being used to track sources and to distinguish old from new sources (8). Studying the selective breakdown of chiral pesticides is also important in relation to their toxicity (9). Previous studies have found that some pesticides are selectively degraded in sewage sludge (10). Addition of sludge to agricultural land can increase the biological activity in the soil, thereby increasing the potential for enantioselective degradation. In this study, the enantiomeric profiles of R-HCH, cis- and trans-chlordane, and o,p′-DDT were investigated, with the aim of establishing whether enantioselective breakdown had occurred in the soil over time or with the addition of sludge. VOL. 35, NO. 10, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
1989
TABLE 1. Summary of Current Status of Selected OC-Pesticides class
name
included in UNECEa
R-HCH β-HCH γ-HCHb DDTs o,p′-DDT p,p′-DDT o,p′-DDD p,p′-DDD o,p′-DDE p,p′-DDE cyclodienes cis-chlordane (CC) trans-chlordane (TC) heptachlore aldrin dieldrin endrin misc HCB endosulfanf HCHs
date of UK legislation
}
} } x
}
x x x x x
}
detected in this study x
1979c,d
x x x
1984c
1992c 1981c 1989c 1989c 1984c 1975c
x x x
x
Past Use of OC Pesticides in the UK. Table 1 provides a list of common OC pesticides and the legislation covering their use in the UK. In the UK, contemporary usage of γ-HCH (lindane) and endosulfan is approximately 100 tonnes/year (11). The other compounds in Table 1 are no longer used in the UK. Estimates of pesticide usage have been compiled by the Pesticide Usage Survey Group (PUSG) of the Ministry of Agriculture, Fisheries and Food (MAFF). These estimates are based on random representative sample surveys of 10 classes of commodity crops (13). These records on annual usage only date back to 1986, although for DDT and γ-HCH the records go back further to 1964. Information on annual usage for these two pesticides is sporadic, probably due to the way it was compiled. However, prior to 1980 DDT usage ranged from ∼20-700 tonnes/year, as opposed to
