Volatile organic compounds in an urban airborne environment adjacent to a municipal incinerator, waste collection centre and sewage treatment plant

Atmospheric Environment 33 (1999) 4309 } 4325

Volatile organic compounds in an urban airborne environment adjacent to a municipal incinerator, waste collection centre and sewage treatment plant J. Leach, A. Blanch*, A.C. Bianchi* Marine and Environment Sciences Research Centre, MEC House, 49 Southcliw Road, Inner Avenue, Southampton SO14 6HR, UK Received 4 December 1997; received in revised form 22 January 1999; accepted 3 February 1999

Abstract The occurrence and temporal distribution of airborne volatile organic compounds (VOC) at nine closely grouped locations in a suburban environment on the edge of the coastline of the Southampton Water estuary, located on the coastline of central southern England, was studied over six monthly periods spanning 1996}1997. The sampling sites circumscribed a juxtaposed municipal incinerator, waste collection and processing centre and sewage treatment plant. Three sets of airborne samples being taken before and after the closure of the municipal incinerator. VOC with volatilities of low to medium polarity ranging broadly from those of n-butane to n-octadecane were the major focus of interest. Over 100 individual compounds were routinely found in localised samples taken during the period of study. The types and concentrations of VOC identi"ed partly re#ect the imprint of the various waste processing operations on atmospheric VOC within the local environment. The most abundant VOC classes consisted of aromatic, chlorinated and organosulphide compounds, with smaller proportions of alkanes, alkenes and cycloalkane compounds. Compounds produced by sewage-processing and waste management operations, including volatile organosulphides and various oxygenated compounds, may occasionally exceed olfactory detection thresholds and represent a source of potential odour complaints in the local urban environment.  1999 Elsevier Science Ltd. All rights reserved. Keywords: Volatile organic compounds (VOC); Thermal desorption; Airborne environment; Alkylbenzenes; Alkanes; Organohalogens; Organosulphides

1. Introduction Within the last decade or so, there has been growing environmental and public health-related concerns over the impact of municipal waste handling processes such as waste incineration, waste collection and reprocessing and treatment plants for human faecal sewage. Each of these activities is associated with the generation of physical, chemical and biologically derived by-products, many of which are di$cult to identify, quantify or assess in terms of their ecotoxicological impacts or their e!ects on hu-

* Corresponding author.

man health and well-being. These concerns have been particularly exacerbated where such activities are sited in close proximity to urbanised areas accommodating housing, schools, shops or related public facilities. As time passes, the impact of such processes on local airborne environments has continued to represent a growing source of scienti"c, toxicological and public health interest. 1.1. Incineration of municipal waste Waste incineration has perhaps been the most intensively studied area as a consequence of the possible links between air pollution products arising from the combustion process and alleged health risks to populations

1352-2310/99/$ - see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 9 9 ) 0 0 1 1 5 - 6

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living within the deposition zone (Eduljee, 1994; Koblantz et al., 1997; Humfrey et al., 1997). As a disposal process, municipal incineration was extensively employed from the late 1960s to the early 1990s. In the last decade, however, general risk assessments have been primarily centred on air contamination issues such as particulate matter `fall-outa, heavy metal deposition on adjacent agricultural land, malodours, generation of toxic organic compounds and their probable e!ects on public health (Humfrey et al., 1997). Focus on the latter has centred on mainly high-molecular weight combustion products in #ue-gases and #y-ash, including polycyclic aromatic hydrocarbons (PAH), polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) (Williams, 1994), and their subsequent transmission into the food chain. Incinerators are also occasionally associated with odour complaints. Such odours are thought to be mainly organic in origin and result from incomplete combustion of organic wastes in the feed (Williams, 1994). Incomplete combustion may also result in quantitatively greater hazardous emissions such as dioxins and furans. However, comparatively little is known about labile, short-lived volatile organic compounds (VOC) which are produced by municipal incinerators, or their occurrence, composition or identity. Although some detailed assessments have appeared in the literature, e.g. (Eduljee, 1994), hitherto, the absence of such information has prevented fuller assessments of their environmental or toxicological signi"cance. Moreover, there is comparatively little information on VOC within local receiving environments in#uenced by incinerator e%uent gases compared to those on particulates, dioxins or metals, or their contribution to urban air pollution. Processes which generate large quantities of volatile organic compounds are of relevance as, when mixed with nitrogen oxides and exposed to sunlight, they aid in formation of photochemical oxidants (ozone and peroxyacyl nitrates), with deleterious implications for air quality. Within the European Community countries, new operating and emission standards for municipal waste incinerators were established in Articles under the EC `Air Framework Directivea (84/360/EEC) and the `Incineration of Municipal Wastes Directivea (89/429/EEC), with a deadline date for compliance by 1st December 1996 (HMSO, 1992). This step led to the closure of many municipal incinerators. In the UK, all but 5 of some 40 plants in the UK were compulsorily closed by the end of November 1996. Current government policies favour construction of new large-scale incinerators which will produce energy (i.e. waste-to-energy) as a by-product of the burning process. New plant will be required to meet new EC emission standards (EC Directive 89/369/EEC), incorporating a limit for Total VOC (expressed as carbon) of 20 mg m\.

1.2. Sewage treatment Sewage treatment and solid waste handling processes are frequently accompanied by the production of nuisance odours, most of which are considered `non-toxica. Faecal wastes evolve a variety of volatile organic compounds and can have an impact on the physiological and psychological well-being of local populations, causing annoyance and disturbance as well as physical symptoms such as nausea, headaches, loss of appetite and a range of other acute and chronic e!ects (Miner, 1980; Schi!man et al., 1995). Prior studies have concluded that complainants living near hazardous waste sites and sewage plants exhibit a higher number of odour-associated symptoms, suggesting a direct relationship between odour and symptomatology (Goldsmith, 1972; Ames and Stratton, 1991; Neutra et al., 1991). Typically, volatile chemical compounds arising from anaerobically generated faecal waste products have low human olfactory thresholds and therefore represent odour nuisance at levels in the partper-billion (v/v) concentration range or below. Many of these VOC include volatile organosulphides and disulphides, volatile fatty acids, amines, p-cresol and a range of heterocyclic compounds (Pain et al., 1991). To date, however, relatively little work has been focused on the identi"cation and quanti"cation of malodorous VOC from sewage wastes in the UK, or their impacts on the receiving environment. 1.3. Municipal waste collection and recycling Municipal waste disposal, collection and recycling sites; and active and historic land"ll sites, represent a further potential source of VOCs which may be associated with release (i.e. through direct emission, evaporation or venting) of residues in materials which have been disposed of (e.g. paints, varnishes, refrigerators, propellants, commercial packaging products) or with the microbiologically mediated onset of decomposition of organic matter in wastes. There have been a number of studies focused in these areas, and the data is well recorded in the literature. Initially, the degradation of refuse materials is dominated by aerobic processes, involving breakdown and consumption by fungi, mites, bacteria and actinomycetes (Allen et al., 1996). As oxygen becomes depleted in compacted waste, anaerobic processes take over, the most important being methanogenesis. The resulting gaseous mixtures evolve not only methane and carbon dioxide, but also many di!erent types of VOC including isoalkanes, alkenes, volatile terpenes and sulphides (Allen et al., 1996). Such volatile products may also be detrimental in terms of their contribution to ground-level air pollution, and in terms of the acute and chronic e!ects on the waste disposal worker's health following inhalation or skin contact with toxic or irritant VOCs. Recent reports have identi"ed the onset of adverse health

J. Leach et al. / Atmospheric Environment 33 (1999) 4309 } 4325

outcomes among residents living near hazardous waste sites, including respiratory disease and related illnesses (Miller and McGeehin, 1997; Muttamara and Leong, 1997), some of which may be related to chronic, low-level exposure to heavy metals, particulates, methane and polycyclic aromatic hydrocarbons. 1.4. Area and objectives of study The area of study selected for this survey was located on the fringe of the Test sub-estuary in Southampton Water, located in central southern England, as illustrated in Fig. 1. This area has been the subject of planning reviews for some years due to intense development along its western shore (New Forest (East) District Local Plan, 1991). This region is well suited for study of anthropogenically-derived airborne VOC as the municipal incinerator and municipal waste processing centre are co-located, and juxtaposed to a sewage treatment plant (Slowhill Copse), which processes raw sewage for the west Southampton Water district. The incinerator was closed down in November 1996 since it did not meet new EC regulations for emission control. It was therefore possible to study local VOC concentrations in the period leading up to, and subsequent to, shutdown of the plant.

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This site has ful"lled a role as a repository for waste for some years. A section of open ground approximately 100 m to the west of the current incinerator was a land"ll site for 30 years prior to the 1970s, receiving wastes including metallic and organic compounds, asbestos and other "brous materials (Bernard, 1998). In the early 1980s, the ground was subject to ecological remediation, which included sealing the original surface with approximately 10 m of soil, and locating methane exhaust vents at strategic locations. It is now an open space recreational parkland. All three municipal processes and their related activities are situated within an area of less than 1 sq km. These facilities are situated on the northern edge of Marchwood, an historic coastal New Forest village currently undergoing rapid urban and industrial development from a rural to a suburban community. The community accommodates approximately 2500 dwellings, of which more than half are less than 15 years old. About 4 km immediately to the north/northeast lies the city of Southampton. The location of the site(s) of interest and the respective sampling locations chosen for this work are shown in Fig. 2. Nine sampling stations were selected, most of which were readily accessible, secure and circumscribe the zone of study.

Fig. 1. The geographical location of Southampton Water and the Solent on the south coast of Great Britain.

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Fig. 2. The location of sampling stations utilised within the VOC survey programmes. (Note: Fig. 2 is not to scale).

Location Key Station 1. Station 2. Station 3. Station 4. Station 5. Station 6. Station 7. Station 8. Station 9.

West of Marchwood (Slowhill Copse) Sewage Treatment Plant (75 m). West of Marchwood Municipal Incinerator (100 m). West of Marchwood Waste Collection, Recycling and Dumping Point (200 m). South of Marchwood Municipal Incinerator (south-facing entrance doors) (100 m). West of Station 4 (approx. 150 m). East of Waste Collection, Recycling and Dumping Point (approx. 75 m) East of Marchwood (Slowhill Copse) Sewage Treatment Plant (approx. 75 m). Northeast of municipal sewage sludge collection and ship pumping point (100 m). Wheat "eld location approx. 300 m south, southwest of the municipal waste processing zone.

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We report the results of six synoptic surveys of airborne VOC spanning the period during which, as a matter of coincidence, the incinerator was closed. Airborne samples were taken on a monthly basis (i.e. "rst day to the last day of each month inclusive) in the months April 1996, July 1996, and September 1996 (corresponding to the time period coincident with the shutdown of the municipal incinerator in November 1996); thereafter December 1996, April 1997 and August 1997. In addition, this work was carried out to provide complementary data on anomolous anthropogenic marine VOC routinely identi"ed in nearby surface estuarine waters, paralleling previous surveys in the immediate area focused on biogenous VOC, e.g. in estuarine channels adjacent to the wastewater plant. Relevant marine VOC research has been reported in the literature within the last decade (Bianchi and Varney, 1988; Bianchi et al., 1989; Bianchi and Varney, 1997, 1998); to which the interested reader is referred. An integral aim was therefore to characterise and quantitate VOC pro"les for future air}sea exchange analysis and subsequent modelling, principally to examine the chemical and structural relationships between anthropogenic and biogenic VOCs at the interface between juxtaposed atmospheric, marine and terrestrial environments.

2. Materials and methods 2.1. Sampling To collect the monthly average samples, passive (i.e. di!usion) sampling methods using Perkin-Elmer ATD4002+ stainless-steel adsorbent tubes (Beacons"eld, UK) were extensively utilised throughout this survey, as described in Brown (1993), Kristensson (1987) and Saunders (1993). Sampling protocols were broadly based on methods and approaches described in current UK HSE methodology for sampling and analysis of VOC by diffusive sampling (MDHS.80, 1995) and within EN standards for sampling and analysis, i.e. BS EN 482 (1994) and BS EN 838 (1996). The methodology adopted in this survey are also based on the techniques cited in the current draft document ISO/CD16017-2 &Air Quality } Sampling and Analysis of VOC by sorbent tube/thermal desorption/capillary gas chromatography } Part 2: Di!usive Sampling' (1998). Passive (di!usive) sampling represents a reliable method for obtaining time-weighted average airborne VOC concentrations and avoids the need for an ongoing dependency on pumped methods (Woolfenden, 1995). Pre-cleaned tubes were packed with 250 mg Chromosorb-1062+ (60}80 mesh) and pre-conditioned by heating at 103C min\ from room temperature to 2503C, thereafter held at 2503C for 10 h. Each tube was then analysed before use to obtain a suitable `#at-baselinea FID chromatogram, indicative of satisfactory pre-

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conditioning. Tubes were then capped with Swagelok2+ storage end caps and sealed under glass in an inert atmosphere until use. Sampling was carried out in duplicate by "tting Perkin-Elmer `golda di!usion caps2+ (incorporating water impermeable membranes) to the air sampling ori"ce and mounting pairs of duplicate tubes under steel `umbrellaa covers at heights of approximately 1.5}2.0 m above ground level. A fuller description of the technical speci"cations of the sampling devices is given in Woolfenden (1995) to which the interested reader is also referred. Samples were also collected occasionally over a period of 12 h (e.g. 0600}1800) using pumped sampling using Accuhaler Model-808 low-#ow sample pumps (MDA, Lincolnshire, IL, USA) attached to Perkin-Elmer adsorbent tubes, packed to the Supelco Corp `Carbotrap 300a speci"cation (i.e. Carbotrap C (250 mg) 20/40 mesh, Carbotrap B (175 mg) 20/40 mesh, Carbosieve SIII (105 mg) 60/80 mesh), supplied by Supelco Inc (Supelco, Bellefonte, PA, USA). These samples were collected at sampling rates of 20$5 ml min\ throughout the sampling duration, and checked for stability every 4 h. A further description of these methods is given in Bianchi and Varney (1992) and Bianchi and Varney (1997). Field blanks were also taken on sampling excursions. Once in the "eld, blank tubes were kept tightly sealed with Swagelok end-caps and attached to each `exposeda pair of tubes. At the end of each sampling period, all samples were collected, sealed with Swagelok end caps and returned to the laboratory for analysis in sealed, pre-cleaned glass jars, and stored in a sample refrigerator at 43C. For "eld blanks, the criteria set in this study was that the mass of artefact peaks was not to exceed 1% of the typical areas of analytes of interest. All analyses was carried out within 18 h of samples being returned to minimise any possible losses of volatiles. Assessments of weather conditions through the period of sampling were also made, spanning the time of sampling. Di!usion parameters were based on available information for ambient environmental sampling drawn from within the scienti"c literature (Brown and Wright, 1994; Wright, 1993) or based on calculation of uptake rates (Perkin-Elmer Application Note, 1995). To check the di!usion performance of the Perkin-Elmer tubes, simultaneous sampling was carried out over 48 h periods by using di!usion tubes and pumped-samples in tandem. Sampling pumps and adsorbent tubes were calibrated to sample at 10 ml min\ and both pumps and pumped tubes changed over every 10 h whilst `in the "elda. Calibration checks were carried out in situ using portable bubble #ow meters and a stopwatch. The pumped and di!usive samples were then analysed and the data compared. Comparisons of a range of compounds including volatile alkanes, aromatics, alkenes, organohalogens and organsulphides yielded coe$cients of variation spanning

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from approximately 0.5}3.0%. The Overall Uncertainty for the di!usive method, as de"ned in EN482, was estimated to be better than 50%, broadly consistent with ISO/CD 16017-2 (1998). Information on suitable uptake rates (long term, ambient) for key compounds was obtained from the HSE Laboratories (She$eld, UK) and Applications Specialist Elizabeth Woolfenden (Perkin Elmer Co, Norwalk, USA). 2.2. Analysis All samples were thermally desorbed on a PerkinElmer automated thermal desorber (ATD50), as described in Bianchi and Varney (1992), and Bianchi and Varney (1997). The technique is well established, and described in Bianchi and Cook (1988), in the PerkinElmer Gas Chromatography Applications Paper No.17 (1990), and in greater detail within Woolfenden (1995). The gas chromatograph was a Perkin-Elmer Series 8500 twin channel FID GC, "tted with data handling facilities. Thermally desorbed components were chromatographed on a cradle-mounted BP-1 chemically-bonded, fused silica capillary column (50 m;0.22 mm ID, 1.0 lm "lm thickness) (SGE Ltd, UK). Detection and quanti"cation of VOC thermally desorbed from the thermal desorber was carried out by FID and mass spectroscopy (Finnigan MAT). Calibration was performed by preparing calibration blends containing approximately 1 g of each material (liquids) or certi"ed gas/vapour standards (gases), gravimetrically introduced (liquids) or pumped (gases/ vapours) into a series of 100 ml volumetric #asks, and carrying out serial dilutions with puri"ed cyclohexane, as has been described in ISO/CD16017-2 (1998). Sub-aliquots were progressively injected onto adsorbent tubes using a linear gas-#ow device operating at 100 ml min\. Calibrations were performed at least six concentration levels spanning the airborne concentrations of interest. The limits of detection were calculated as being 3p /m, where p is the standard deviation of

the blank response and m is the slope (or sensitivity) of the calibration graph for the analyte in question. The lower limit of detection for the sampling and analytical method was estimated to be approximately 0.01 ng l\, determined for the GC}MS analytical protocol, for most compounds of environmental and toxicological interest. The lower limit of detection for GC}FID analysis was also determined as (0.01 ng l\, for all alkane, alkene, aromatic, chlorinated and organosulphide compounds. In addition, externally-sourced calibration standards prepared on Perkin-Elmer tubes for &environmentallevel' concentrations (i.e. 1}2 lg tube\) were obtained via the HSE workplace analysis scheme for pro"ciency (WASP) and from suppliers of certi"ed reference materials (e.g. NMi, Holland). These standards were used at the

beginning and at the end of each of the analytical exercises. Mass spectral analysis was carried out using a Finnigan-MAT 4500 Quadropole high-resolution mass-spectrometer and a low-resolution Finningan MAT ion trap detector (ITD), utilising the spectrometers in full-scan mode, and occasionally in SIM mode (for speci"c compounds, e.g. semi-volatile PCBs). The basic operating conditions were similar on both mass spectrometers: Mass range: 35}300 atomic mass units; Scan Time: 0.5 s scan\; Photomultiplier Delay: 200 s; Nominal Electron Energy: 70 eV in electron impact (EI) ionisation mode; Transfer Line Temperature: 250}3003C; Ion Source Temp: 2503C; GC-to-MS transfer line interface: Open-split mode. The determination of compound identity was determined by use of mass-spectral libraries, including NBS, General Purpose and NIST library searching. In addition, co-injection of certi"ed calibration standard mixtures obtained from Supelco (Poole, Dorset, UK) and Aldrich Ltd (Gillingham, Dorset, UK) and Chrompack UK (Millharbour, London, UK) was used to determine identity and similarities in functional group and molecular structure. Throughout the sampling and analysis programme, checks were made using gravimetrically spiked aliquots of multicomponent standards, internal standards, surrogate compounds (Aldrich Ltd, and TNO Laboratories, Holland) and blanks were injected onto prepared adsorbent tubes, on an ongoing basis. In summary, the method allowed the determination of volatile organic compounds spanning a broad range of compounds with boiling points ranging from C to C .   3. Results and discussion Volatile organic compounds were detected at each of the nine sampling stations over the six one-monthly sampling periods, total VOCs ranging broadly from 100}1300 lg m\. The mean monthly total VOC concentration data for each station is shown in Fig. 3(a) and (b), respectively, covering the period during which sampling took place. The principal VOC sub-classes identi"ed were aromatics, alkanes and alkenes (including straight-chain and cyclo-compounds), organohalogens, organosulphides and oxygenates (i.e. aldehydes, alcohols, ketones). The relative abundance of these compounds, presented as the arithmetic mean concentrations of the main volatile compound sub-classes ($1 standard deviation), are shown in Table 1. Organohalogen and aromatic compounds

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Fig. 3. (a) Mean monthly total VOC concentrations for sampling stations SS-1}SS-9 inclusive for April 1996, July 1996 and September 1996 (i.e. pre-incinerator shutdown). All concentrations are in ng l\ (i.e. lg m\). (b) Mean monthly total VOC concentrations for sampling stations SS-1}SS-9 inclusive for December 1996, April 1997 and August 1997 (i.e. post-incinerator shutdown). All concentrations are in ng l\ (i.e. lg m\).

were the most proli"c in the vicinity of the waste processing zone, paralleling the distribution of VOC in nearby estuarine surface waters documented by Bianchi and Varney (1998). In most cases, more than 100 individual volatile organic compounds were recovered, as illustrated by the specimen gas-chromatographic trace

(cGC-FID) shown in Fig. 4 (Sample Station 4, September 1996). A numbered listing of the compounds identi"ed is included in Table 2. The data suggest that, for at least the "rst three months of the survey, stations in relatively close proximity to the waste control site(s) (i.e. Stations SS4, SS5, SS6) may

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SS3 SS2 SS9 SS8 SS7 SS6 SS5 SS4 SS3 SS2

Sampling data (n"3) (Pre-incinerator shutdown) Sampling station

VOC compound sub-class C4 } C18 Alkanes#Alkenes Aromatics Organohalogens Organosulphides Oxygenates VOC

SS5 SS1 SS1

SS4

Arithmetic mean concentration $1 S.D. Arithmetic mean concentration $1 S.D.

Sampling data (n"3) (Post-incinerator shutdown)

SS6

SS7

SS8

SS9

J. Leach et al. / Atmospheric Environment 33 (1999) 4309 } 4325 Table 1 Summary of concentration data obtained from analysis of du!usive airborne samples during the 1996/97 surveys. (All concentrations are expressed as the arithmetic mean concentration $1 S.D. in lg m\)

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have been directly or indirectly in#uenced by processing activities. The mean concentration range of aromatics were between 131 and 285 lg m\ and for organohalogens, between 197 and 396 lg m\. For the entire data set, the highest recorded VOC concentrations for this period were measured at SS4 (mean monthly concentrations ranged from 939 to 1205 lg m\). VOC concentrations were also moderately elevated at SS5, approximately 200 m due east, northeast of SS4 (monthly concentrations ranging from 929 to 1008 lg m\). Typical concentration data from the other sample stations ranged broadly from 200 to 976 lg m\, with the lowest VOC concentrations (e.g. sample stations SS3, SS9 and SS8) tending to correspond with locations furthest from the waste processing activities. The concentration ranges observed here are within the same order of magnitude as those reported by Ciccioli et al. (1992) for VOC-containing urban air in the city of Rome, and broadly similar to those reported by Bianchi and Varney (1992) in a similar study of marine VOC air}sea exchange rates within the local area. Broadly, VOC levels below approximately 100}150 lg m\ may be regarded typical of relatively uncontaminated air, moreso if the VOC are biogenic and do not contain signi"cant levels of anthropogenic compounds such as aromatics or organohalogens (Ciccioli, 1993). Chronologically, VOC concentrations at all stations appeared to increase through April 1996 to September 1996, except at SS4 and SS5, where the total VOC was marginally reduced during July 1996. A broadly similar seasonal #uctuation in VOC pro"les was observed by Bianchi and Varney (1992), who assigned this phenomenon to the relationship between sources (e.g. tra$c-related sources of VOCs), and sinks (i.e. removal mechanisms linked to meteorological conditions, including processes such as photodegradation and adsorption) leading to seasonally variable VOC concentrations in the lower atmosphere. Overall, the concentration data relating to the three sets of monthly samples obtained in the last 3 months of the survey suggested a net reduction in total mean VOC levels. Here, the stations in proximity to the waste processing areas (SS4, SS5 and SS6) appeared to have decreased markedly in their total VOC content. Overall, the mean monthly VOC concentrations at SS4 for the three sampling months were approximately 50% of the "rst 3 month survey mean monthly concentrations. This general pattern was also seen at SS5, indicating that the cessation of incinerator-related activities may have had an ameliorating in#uence on anthropogenic VOC concentrations. A comparison of pre- versus post-shutdown concentrations is shown in Fig. 5, comparing mean VOC concentrations at a close-proximity sampling area (i.e. SS5) with a sampling area located more distantly (i.e SS9, approx. 300 m south, southwest). Fig. 5 also illustrates the relative reductions in volatile

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Fig. 4. Representative cGC-FID chromatogram of VOC identi"ed at Sample Station 4, located 100 m south of Marchwood municipal incinerator (September 1996). Peak identi"cations are given in Table 2.

aromatics and organohalogens post-shutdown, against those at SS9. A highly diverse range of volatile organic compounds was identi"ed during these surveys. Some VOC identi"ed in the waste processing zone environment were not commonly encountered in marine VOC surveys for the Southampton estuary by Bianchi and Varney (1992). Importantly, in many other cases, anthropogenic VOC inexplicably detected in otherwise uncontaminated surface water bodies nearby were identi"ed at elevated concentrations in contiguous air available for exchange and mixing. These observations might suggest that VOC species that may be generated or released by waste-associated processes (e.g. chloroform, tetrachloroethylene, toluene) are rendered readily available for air-to-sea transfer due to their physicochemical characteristics (e.g. Henry's Law Constant, aqueous solubility). An inventory of the most commonly encountered VOC compounds of interest is listed in Table 3. Within the broad suite of VOC shown in Table 4, various patterns of speci"c environmental interest occur within the individual sub-classes (or functional groupings) of compounds. These features may be useful for characterising sources, and serve as markers for assessing potential impact on local air quality. VOC are ubiquitous in urban and sub-urban environments, but the identity and concentration ranges of VOC associated with waste processing activities might facilitate understanding of potential health e!ects on local communities.

3.1. Volatile aromatics Over 20 aromatic VOC were regularly recovered in all air samples. The principal compounds were benzene, toluene, C2-alkylbenzenes, C3-alkylbenzenes, C4-alkylbenzenes and volatile PAH including naphthalene and alkyl-naphthalenes (e.g. 1,2- and 1,4-dimethyl naphthalene). The mean arithmetic airborne concentrations of volatile aromatics are presented in Table 3. The concentrations of volatile aromatic compounds appeared to vary throughout the sampling study. Traf"c-derived VOCs, associated with a high density of vehicle movements, is likely to be a ubiquitous source of aromatics, and are likely to have been a key source. Waste handling activities (i.e. transportation of wastes, recycling) attracted a large daily tra$c burden at the entrance roads to the incinerator and juxtaposed waste dump (e.g. up to several thousand car and heavy goods vehicle movements per day between the hours of 0700 and 2100). Waste handling activities may also have contributed to the presence of volatile aromatics. In the earlier stages of monitoring, corresponding broadly to the period prior to incinerator shutdown, the relative component ratios for stations in proximity to the incinerator (e.g. SS4) were: [benzene (0.20): toluene (0.30): C2-alkylbenzenes (0.28): C3-alkylbenzenes (0.19): C4-alkylbenzenes (0.03)]. At sites further away, and thus theoretically less impacted by waste processing activities relative to tra$c contributions

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Table 2 Representative VOC identi"ed at Station SS4. Identi"cation numbers refer to the cGC-FID chromatogram shown in Fig. 4 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) (40) (41) (42) (43) (44) (45) (46) (47) (48) (49) (50) (51) (52) (53) (54) (55) (56) (57)

2-Methylpropane n-Butene 1,3-Butadiene n-Butane Methyl mercaptan Chloroethane Fluorotrichloromethane (F.11) Isopentane 2-Methylbutane 2-Methylbutene-1 2-Methyl-1,3-butadiene n-Pentane Ethyl mercaptan Dimethylsulphide 2-Methyl-2-butene Dichloromethane Carbon disulphide Freon-113 Propanal Propanol-1 Propyl mercaptan 2,2-Dimethylbutane 2,3-Dimethylbutane methyl-tertiary butyl ether (m TBE) 2-Methyl pentane 3-Methyl pentane Butanone-1 n-Butanal n-Hexane Pentanone-2 Trichloromethane (chloroform) 2-Methyl pentene-1 2-Methylfuran 1,2-Dichloroethane 1,1,1-Trichloroethane Carbon tetrachloride Ethanol Benzene Butanone-2 Cyclohexane Propanol-2 2,2,3-Trimethylbutane Thiophene Bromodichloromethane Trichloroethylene Diethylsulphide 2,5-Dimethylfuran Butanethiol n-Heptane 2,2,4-Trimethylpentane Methylcyclohexane 2,2,4-Trimethylpentene-2 Pentanal Mercapto acetic acid Dimethyldisulphide Methylbenzene (Toluene) 2-Methylthiophene

(58) (59) (60) (61) (62) (63) (64) (65) (66) (67) (68) (69) (70) (71) (72) (73) (74) (75) (76) (77) (78) (79) (80) (81) (82) (83) (84) (85) (86) (87) (88) (89) (90) (91) (92) (93) (94) (95) (96) (97) (98) (99) (100) (101) (102) (103) (104) (105) (106) (107) (108) (109) (110) (111) (112) (113) (114) (115) (116) (117) (118)

1-Chloro-2,3-epoxypropane n-Butanol Chlorodibromomethane Methyl isobutylketone 1,1,2,2-Tetrachloroethylene Octene-1 n-Octane Hexanal 2,2-Dimethylheptane Ethylbenzene 1,3-Dimethylbenzene 1,2-Dimethylbenzene Chlorobenzene Tribromomethane Styrene Dimethytrisulphide n-Nonane Nonene-1 Heptanal Isopropylbenzene a-Pinene Camphene 1,5-Cyclooctadiene Cyclooctene 2,4-Dimethyl-4-vinylcyclohexane n-Propylbenzene l-Chloroheptane n-Decane Benzaldehyde 1,2-Dichlorobenzene p-Cymene 1,3,5-Trimethylbenzene 1-Ethyl-2-methylbenzene 1,2,4-Trimethylbenzene Octanal Limonene 1,2,3-Trimethylbenzene 2,3-Dihydroindene Indene 1-Chlorooctane 1,2-Dichlorobenzene n-Undecane 1-Methyl-3-propylbenzene 1-Methyl-2-propylbenzene 1,4-Dimethyl-3-ethylbenzene 1,3-Dimethyl-3-ethylbenzene 2-Dimethyl-4-ethylbenzene 1,3-Dimethyl-4-ethylbenzene 1,2,3,5-Tetramethylbenzene 1,2,3,4-Tetramethylbenzene n-Dodecane Naphthalene 1-Chlorodecane n-Tridecane 2-Methylnaphthalene 1-Methylnaphthalene Biphenyl Indole (benzo(b)pyrrole) Indole-3-acetic acid 1,2-#1,3-Dimethylnaphthalene Skatole

J. Leach et al. / Atmospheric Environment 33 (1999) 4309 } 4325 Table 2 (Continued) (119) (120) (121) (122) (123) (124) (125) (126) (127) (128) (129) (130) (131) (132}141) (141}148)

n-Pentadecane n-Hexadecane 1-Phenyldecane Pristane n-Heptadecane n-Dodecylbenzene n-Octadecane Phytane Tridecylbenzene a C aldehyde  n-Nanodecane Phenanthrene a C phenylated ether  Mixture of C }C iso-alkenes and   cyclo-alkenes Mixture of C }C alkyl phenylated   compounds

alone, the relative abundance of aromatics was: [benzene (0.14): toluene (0.34): C2-alkylbenzenes (0.31): C3-alkylbenzenes (0.20): C4-alkylbenzenes (0.01)] broadly consistent with ratios quoted by Ciccioli et al. (1992) for urban tra$c. During monitoring which took place in the period after closure of the incinerator, the net concentrations of aromatics were apparently coincidentally reduced. Also, the ratios of aromatics for stations closest to

4319

the waste processing site(s) were altered, corresponding somewhat more closely with those found at locations further from the site. In particular, the ratio of benzene/toluene altered from approximately 0.66 to 0.41. The empirical or statistical signi"cance of the variance in the ratios observed, despite their potential interpretive value, cannot be more closely or reliably determined without further data points, which closure of the incinerator now precludes. There is therefore no direct evidence to suggest that municipal combustion operations may be responsible for existing volatile aromatic levels in the surrounding environment. However, as a matter of note, measured concentrations of volatile aromatics in excess of &background' levels have been previously reported in emissions from incinerators burning hazardous wastes, occurring as products of incomplete combustion. Such a pathway was proposed by Eduljee (1994), who suggested an in situ decomposition mechanism, in the co-presence of simple C4 hydrocarbons and chlorinated hydrocarbons, which yields benzene as an end-product, i.e. CH CH#C HClPC H #Cl,     C H #(H, Cl)PC H #(H , HCl),      C H PC H #H.     Further addition of C species to the C alkane, followed   by cyclisation and dehydrogenation of the intermediates,

Fig. 5. Mean concentrations for the VOC Sub-classes (Aromatics, Alkanes/Alkenes, Organohalogens, Organosulphides and Oxygenates) at SS5 and SS9, showing typical pre-incinerator shutdown and post-incinerator shutdown concentrations. All concentrations are in ng l\ (i.e. lg m\).

4320

J. Leach et al. / Atmospheric Environment 33 (1999) 4309 } 4325

Table 3 Airborne concentration ranges for VOC in ambient air from sample stations SSI}SS9 inclusive. All results are expressed in lg m\ Volatile organic compound

Concentration range Min}Max/lg m\

Volatile aromatics Benzene Toluene Ethylbenzene m-, o-, p-Xylenes C3-alkylbenzenes C4-alkylbenzenes Naphthalene Alkyl naphthalenes

5.1}136.9 24.7}191.8 11.5}26.7 45.6}169.4 11.1}123.5 0.5}6.8 0.6}27.2 12.3-69.3

Volatile alkanes and alkenes Ethane#ethene Propane#propene Butanes 1,3-Butadiene C5}C15 alkanes C5}C15 cycloalkanes C5}C15 alkenes C5}C15 cycloalkenes

0.3}18.6 1.3}29.4 23.2}49.3 3.4}33.4 59.4}57.5 32.2}56.7 35.6}76.5 12.2}34.5

Volatile organohalogens Freon-11 Freon-12 Freon-113 Freon-115 Chloromethane Chloroethane (ethyl chloride) 1-, and 2-Chloropropane 1-Chlorobutane 2-Chloro-1,3-butadiene Dichloromethane 1,1,1-Trichloroethane Trichloromethane (chloroform) 1,2-Dichloroethane Trichloroethylene Tetrachloroethylene Chlorobenzene 1,2-Dichlorobenzene 1-Chloro-2,3-epoxypropane Chlorodibromomethane 2,3-Dichloro-1,1biphenyl (PCB) 3,4-Dichloro-1,1biphenyl (PCB) 2,3,4-Trichloro-1,1-biphenyl (PCB) 2,2,5-Trichloro-1,1-biphenyl (PCB)

0.6}24.3 0.7}46.5 1.2}22.2 2.3}13.2 1.3}24.3 0.2}28.5 0.3}26.7 0.4}23.3 0.5}11.2 0.6}27.3 0.7}23.3 0.8}23.3 0.9}21.1 1.2}35.3 1.3}33.2 2.3}37.2 0.2}23.2 0.3}11.1 1.2}20.2 0.2}33.2 0.3}27.2 0.4}32.2 0.4}27.2

Volatile organosulphides Methanethiol Ethanethiol Propanethiol Butanethiol Dimethylsulphide Dimethyldisulphide Dimethyltrisulphide Mercaptoacetic acid

3.3}68.4 3.4}56.4 2.3}45.4 2.4}36.6 3.4}42.3 2.0}39.3 1.2}28.6 1.3}34.6

Miscellaneous VOC Acetaldehyde Acrolein Propionaldehyde Propanal Butanal Pentanal Hexanal Heptanal Benzaldehyde Acrylonitrile 2-Methyl furan 2,5-Dimethyl furan 2-Furoic acid Dimethylformamide Thiophene 2-Methyl thiophene Styrene Indene 2,3-Dihydeoindene Indole (benzo(b)pyrrole) Indole-3-acetic acid 3-Methyl lindole (skatole) Mono butyl phthalate Di-n-Octyl phthalate o-Dimethyl phthalate Acetic acid 2-(4-Chlorophenyl) thiazole-4-acetic acid Iso-Valeric acid n-Valeric acid (pentanoic acid) Isobutyric acid Butanoic acid p-Cresol Phenyl butyric acid a Dimethyl benzoic acid Biphenyl 3,3-Dimethyl-1,1-binaphthyl Lactic acid methyl ester Pent-4-en-2-ol Methyl isobutyl ketone Alanine Methyl ester of alanine Hydroxylamines Methyl-n-butylamine Methylisobutyl amine

(0.1}32.2 1.2}25.4 (0.1}13.2 (0.1}14.4 (0.1}18.5 (0.1}23.2 1.3}23.2 1.4}14.3 1.5}26.5 (0.1}12.2 (0.1}12.3 (0.1}23.4 (0.1}10.2 1.2}14.2 (0.1}29.3 2.2}13.4 (0.1}25.5 2.2}11.2 (0.1}23.3 (0.1}34.4 4.5}39.3 3.5}26.3 (0.1}32.1 (0.1}25.4 (0.1}20.2 4.3}23.3 2.2}2.5 3.3}53.2 4.5}13.3 5.4}38.6 2.1}27.8 (0.1}24.5 (0.1}38.7 (0.1}34.5 2.2}37.5 1.1}45.4 (0.1}21.1 (0.1}23.2 (0.1}2.1 (0.1}34.3 (0.1}12.2 (0.1}38.6 3.3}36.3 4.5}22.3

results in the formation of the benzene compound. In the Southampton district, background ambient levels of benzene have been reported by Bevan et al. (1991), who recorded concentrations between 37 and 76 lg m\ benzene in urban and suburban areas within the city environment. Southampton is also included within the UK Automatic Urban Network of hydrocarbon sites, sponsored by the UK Department of the Environment, Transport and Regions (DETR). For example, data for benzene are published by the National Centre for Environmental Technology on the worldwide internet. Typical published data range from 1 to 15 lg m\, although concentrations

5.9 27.2 26.3 17.7 0.3 16.6 46.2 52.4 32.7 0.5 35.1 94.4 86.7 52.9 1.0 46.4 114.2 165.3 100.2 1.2 12.3 30.1 39.2 25.1 0.7 19.5 56.2 47.4 30.3 0.9 20.7 50.7 46.4 29.7 1.2 6.6 28.7 28.4 19.9 0.6 17.3 47.1 49.9 30.1 1.0 40.2 57.5 60.2 40.9 2.8 59.4 62.5 68.3 46.5 1.2 80.7 75.0 81.1 52.7 4.9 120.6 182.4 170.1 111.1 15.4 14.1 39.2 42.3 28.9 0.8 16.1 50.7 52.3 33.3 2.2 VOC compound sub-class Benzene Toluene C2-alkylbenzenes C3-alkylbenzenes C4-alkylbenzenes

15.3 45.2 49.4 32.1 1.3

SS8 SS7 SS6 SS5 SS4 SS3 SS1 Sampling station

SS2

30.3 77.1 69.9 47.5 1.1

21.4 61.2 65.9 43.1 0.7

SS9 SS8 SS7 SS6 SS5 SS4 SS3 SS2 SS1

Arithmetic mean concentration/lg m\ Arithmetic mean concentration/lg m\

SS9

Sampling data (n"3) (Post-incinerator shutdown) Sampling data (n"3) (Pre-incinerator shutdown)

Summary of concentration data for volatile aromatic hydrocarbons obtained from analysis of di!usive airborne samples during the 1996/1997 surveys. (All concentrations are expressed in lg m\)

Table 4

J. Leach et al. / Atmospheric Environment 33 (1999) 4309 } 4325

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up to approximately 50 lg m\ have been recorded on the database from time to time. Overall, benzene levels are probably comparable with those typical within other European urban and city centres (Ciccioli et al., 1992); and in the internal cabin environment(s) of motor vehicles using busy commuter roads (Du!y and Nelson, 1997). 3.2. Volatile organohalogens Volatile organohalogen compounds represented a proli"c group of VOC identi"ed. Although concentrations of individual organohalogens rarely exceeded 30}35 lg m\, a broad variety of volatile chlorinated compound species were identi"ed. At some stations, total volatile organohalogen concentrations were up to 10 times higher than concentrations of identical compounds recorded by Eduljee (1994) in a similar study of combustion-derived VOC. Volatile organohalogens are likely to be associated with a range of waste management processes. Some organohalogens derive from chlorine-containing waste products as simple thermal decomposition products (Williams, 1994). Compounds identi"ed included chloromethane, dichloromethane, 1,2-dichloroethane, chloroform, tetrachloroethylene, carbon tetrachloride and various alkylated chlorobenzenes. These compounds were reported by Eduljee (1994) in incinerator #ue gases, formed by the recombination of molecular fragments resulting from pyrolysis or partial oxidation of waste constituents. Further compounds encountered here included chloroethane, chloropropane, chlorobutane, 2-chloro-1,3-butadiene, 1-chloro-2,3epoxypropane and semi-volatile poly chlorinated biphenyls (PCBs). Typical PCB concentrations were approximately 0.1}35 lg m\, and veri"ed by further mass-spectral calibration using `primarya PCB standards. PCBs are not thought to be normally present in municipal waste incineration wastes, although they may occur if, for example, sewage sludges or other PCBcontaining wastes form part of the feed. Chloroform (i.e. trichloromethane) was also commonly found, and measured at concentrations ranging from 0.17 to 23.3 lg m\. These observations may be correspondent with measurements made by Bianchi and Varney (1997, 1998) who identi"ed chloroform in aerosols and o!-gassing VOCs associated with sewage-bearing surface waters in localised water treatment plant, and in sur"cial marine sediments within the principal particle deposition zones. Freons (e.g. Freon 11, Freon-12, Freon 113) were also identi"ed. Freons are ubiquitous, common VOCs in many city environments, particularly in the vicinity of waste management and processing operations. They may be released locally from the deposition of old refrigerators, cooling units, and small industrial devices which utilise Freons. Freon recovery processes are not routinely

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J. Leach et al. / Atmospheric Environment 33 (1999) 4309 } 4325

employed as part of the municipal waste site activities, which may facilitate release of the waste gases during compaction, crushing or cutting-up of freon-containing equipment. 3.3. Volatile alkanes/alkenes Volatile alkanes and alkenes were commonly found. Methane, C and C hydrocarbons may occur as waste   products from incinerators, usually found at much higher concentrations than chlorinated compounds (Eduljee, 1994). In this study, C and C hydrocarbons were found   at comparable concentration levels (0.3}18.6 lg m\; 1.4}29.4 lg m\, respectively). The sources of these compounds are necessarily speculative. Although motor vehicles and other combustion sources may be reasonably implicated as key sources, o!gassing from the nearby historical dumpsite could not be excluded as a source. (nb: methane was not detectable using the &Carbotrap 300' adsorbent tube speci"cation in the sampling method employed). Volatile terpene compounds were also consistently identi"ed, although these may in part emanate from plantations of deciduous and evergreen trees which occur in profusion within the overall study area. The principal terpene compounds found included d-limonene, 1,5-cyclooctadiene, b-terpinene, myrcene, camphene and a-terpinene. Trees are abundant sources of volatile terpenes, particularly in autumn months (Altshuller, 1983). Most compounds were present at relatively low absolute concentrations (0.01}2 lg m\). Waste plant-based material (e.g. trees, shrubs, leaves) are stored, compressed and recycled at the waste collection centre, and it is possible that early stages of aerobic and anaerobic plant matter decomposition may also contribute to the presence of terpenes. 3.4. Volatile organosulphides Volatile organosulphides were mainly comprised of volatile thiols (mercaptans) and alkylsulphides (e.g. dimethylsulphide, dimethyldisulphide). The major source of airborne organosulphides was thought to be the sewage treatment plant. Many compounds arise from fermentation processes occurring within sewage plants including hydrogen sulphide, sulphydryls and higher molecular weight sulphides. Associated bacterial action is frequently anaerobic and exothermic, and due to the high sulphate content in human faeces, there are rich sources of sulphur molecules from which organsulphides may be subsequently generated. The Marchwood sewage plant serves approximately 100,000 persons on the western fringe of the Southampton Water estuary (New Forest District Local Plan Document, 1991). According to Summer (1971), typical sewage farms will process 2.6 g of sulphate day\ per head of population,

yielding more than 0.25 t of sulphate day\ for every 100,000 people. The Marchwood (Slowhill Copse) Sewage Plant has given rise to frequent malodour complaints over the last decade, increasing in frequency when the plant increased its waste capacity (and loadings) by 35% in the late 1980s (New Forest District Local Plan Document, 1991). The majority of complaints occur in summer months, when air temperatures are high, and wind direction is toward the urban areas, thus increasing the likelihood of malodorous VOCs being transported towards the population centre. Considering the most highly malodorous compounds; concentrations approaching 70 and 57 lg m\ were recorded for methanethiol and ethanethiol, respectively, and 40 lg m\ for dimethyldisulphide. Methanethiol, ethanethiol and dimethyldisulphide have low olfactory thresholds (i.e. below approximately 100, 6 and 12 lg m\, respectively (Verscheuren, 1983)), most of which could be exceeded, thus indicating a substantive nuisance impact on the receiving population. A partial explanation of the availability of malodorous low-molecular weight organosulphides was provided by Bianchi and Varney (1997), who showed that volatile thiols have very high transfer coe$cients (i.e. waterPair transfer rates), e.g. methanethiol: K "13.66 cm h\, from surface 2 waters in sewage bays, to air. This results in high #ux rates, thus illustrating the potential to constitute fugitive emissions from sewage processing works. Further malodorous compounds such as indole, skatole (3-methyl indole) and indole-3-acetic acid were identi"ed in samples downwind from the sewage plant. Indole and skatole represent substances which constitute a `characteristica sewage odour (Summer, 1971) and may give rise to olfactory o!ence at concentrations below 0.01 lg m\. Skatole is frequently associated with unpleasant odours emanating from pig farm slurry. Indole-3-acetic acid is primarily used as a plant growth hormone, but may also be found in secondary domestic sewage plant e%uent. Its identi"cation in air samples obtained from sewage plants also highlights the potential for semi-volatile materials to migrate outwards (possibly as a vapour or as aerosols) into communities, as emphasised by Miller and McGeehin (1997) in their study of populations living in proximity to waste sites. 3.5. Miscellaneous VOC A broad assemblage of further VOC subclasses were detected, in addition to the principal VOC groups discussed above, as listed in Table 3. (i)

Volatile aldehydes were proli"c in air samples from the sewage treatment plant. Many of these (e.g. propanal, butanal, pentanal) arise from decomposition

J. Leach et al. / Atmospheric Environment 33 (1999) 4309 } 4325

of faeces or organic plant matter. The most abundant aldehyde, benzaldehyde, ranged from 1.5to26.5 lg m\, and probably arises mainly from decaying organic material. Other aldehydes, including the pungent, acrid compound, acrolein (2-propenal), may be linked to waste combustion. Acrolein concentrations spanned from 1.2 to 25.4 lg m\. (ii) Phthalate compounds (e.g. mono butyl phthalate) are associated with burning of plastics, dyes, medicines and some synthetic perfumes. (iii) Organic acids (e.g. n-valeric and iso-valeric acid, butanoic acid), possibly linked to sewage treatment plant processes. Many of these compounds have both synthetic origins (#avours, perfumes) and are also formed as unpleasant, malodorous fermentation products in waste organic matter treatment plants. Acids such as acetic acid, butanoic acid and valeric acid have been reported in both human and pig faecal slurries, often contributing to community odour complaints (Pain et al., 1991) Up to ten separate volatile acids were detected in concentrations between 0.1 and 40 lg m\.

4. Summary and conclusions This study represents a broad overview of the occurrence, and temporal and spatial variation of VOC identi"ed in an area occupied by a juxtaposed municipal waste incinerator, sewage treatment plant and waste collection and recycling centre. The main conclusions of this study were as follows: (1) A broad range of anthropogenically derived airborne VOC were identi"ed in six sets of monthly samples taken from nine pre-selected sampling stations (n"54 samples) within the zone of interest. The sampling programme incorporated three sets of samples taken spanning an eight-month period coinciding to a time interval prior to the shutdown of the incinerator, and a further set of samples within an eight-month span following shutdown of the incinerator. More than 100 individual VOC were typically identi"ed in the samples. (2) In terms of relative abundance, volatile compound sub-classes occurred in the broad succession of (i) organohalogens, (ii) aromatics, (iii) alkanes/alkenes, (iv) organosulphides, and (v) oxygenates. The range of total VOC concentrations spanned 100}1300 ng l\. The highest recorded range of VOC concentrations were identi"ed at three sample stations (i.e. SS4, SS5 and SS6) located in closest proximity to waste processing centres. (3) An apparent lowering in total VOC concentrations was observed in the period corresponding to the

(4)

(5)

(6)

(7)

4323

closure of the incinerator. The greatest reductions (i.e. ca. 50%) occurred at the three sample stations (i.e. SS4, SS5 and SS6). In excess of 10 volatile aromatic compounds and 20 volatile organohalogen compounds were recovered in air samples. The greatest diversity in compound type occurred in sample stations in general proximity to the waste processing activities, mainly within 100}200 m. A variety of organohalogens were identi"ed, incorporating a range of chlorinated solvents and chlorine-containing organic volatiles. Some of these included PCBs. Freon compounds were also encountered. Volatile organosulphides were found at levels which may represent a source of odour and nuiance complaints in the vicinity, in tandem with key malodorous compounds such as skatole and aldehydes (e.g. iso-valeric acid). The data indicate some validation of previous VOC air}sea exchange studies, supporting the premise that localised airborne sources, linked to waste processing activities, may account for the identi"cation of non-marine anthropogenic VOCs in low-salinity estuarine surface waters strongly characterised by otherwise biogenically derived VOC, through weather-mediated air-to-water transfer processes and/or direct transfer into the water column.

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