Chemosphere, Voi.24, No.9, pp 1207-1216, 1992 0045-6535/92 $5.00 + 0.00

Printed in Great Britain Pergamon Press Ltd

CONCENTRATIONS AND TO)~ICOLOGICAL SIGNIFICANCE OF TRACE ORGANIC COMPOUNDS

IN MUNICIPAL SOLID WASTE LANDFILL GAS

T. Assmuth" and K. Kalevi

Water and Environment Research Institute

PO Box 250, SF-00101 Helsinki, Finland

ABSTRACT

Concentrations of over 30 aromatic and halogenated aliphatic trace organic contaminants were measured in gas samples from wells in 3 old and 1 active municipal landfills in Southern Finland. The concentrations of several chloromethanes, chloroethenes and aromatic compunds reached ca. 100 mg/m 3, exceeding urban background levels by up to 100 000 times. There was considerable intersite variation in concentrations. Occupational health norms and reportedly toxic concentrations were occasionally exceeded by carbon tetrachloride in particular. The rough estimates of dominant contaminant emissions from the study sites were of the order of kg/d, exceeding respective waterborne fluxes. The toxicological significance of these and other published data is discussed.

INTRODUCTION

Increasing concern has been directed to the generation, quality and effects of gases formed in landfills and other

waste deposits. There are several interacting reasons for this interest.

First, landfill gas reflects the properties of the wastes. Thus, main gas components give insight in waste

decomposition processes (e.g., Farquhar & Rovers 1973, Baccini et al. 1987), and trace gases serve as an indicator

of volatile contaminants in the waste.

Second, information on landfill gas quality is important in the expanding treatment and use of landfill gas. In

addition to the explosive main gas component methane, minor constituents may affect gas treatment systems

through corrosion, and harmful substances in treatment products pose environmental and safety problems (Young

& Blakey 1991, Wilhelm 1991).

Third, landfill gas quality is of occupational health concern. Apart from explosion hazards, landfills workers

are exposed to hazardous gases as well as dust particles.

Fourth, landfill gas impacts the environment in several ways. Methane may cause explosions in adjacent

structures, requiring cautious safeguarding techniques (Campbell 1987), and may damage landfill vegetation.

Odorous gases cause nuisance in the environment (Baldwin & Young 1991). More importantly, concern has been

caused by the global role of gases from waste disposal in the alteration of atmospheric quality (e.g., Thorneloe

1991). Finally, toxic airborne substances cause local environmental risks of acute or long-time effects.

Information on toxic organic compounds in landfill gas has been published recently (e.g., Brookes & Young

1983, Wood & Porter 1987, Rettenberger & Stegmann 1991, Young & Blakey 1991). Additionally, landfill

emissions have been characterized by ambient air sampling (e.g., Harkov et al. 1985, Lewis et al. 85, Stephens et

al. 1986). However, relevant field data on, and evaluations of, the concentrations of trace organics in.landfill gases

are still insufficient, especially as regards Finnish conditions. As part of a research project addressing the environ-

mental risks of hazardous substances in Finnish landfills (Assmuth el al. 1990), the concentrations of a number of

priority pollutants in municipal landfill gas were measured and preliminarily assessed.

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1 2 0 8

SITES AND M E T H O D S

Study sites

The study sites include active and terminated municipal landfills of variable contents and properties, most of them small

(Table 1, Fig. 1). Land filling techniques are typically poor, and so are the data on fill construction. In all of the sites,

codisposal of industrial, hazardous or other special wastes with mixed municipal wastes is reported or assumed to have

taken place. In some fills separate sections or final covers exist. Gas collection systems have not been installed.

Table 1. Basic characleristics of the studied landfills.

Characteristic S ~ t e

(unit)

Sulkavuori Domarg~rd Mankkaa Kujala

Municipality Tampere Porvoo Espoo Lahti

Operation status terminated terminated (par 0 terminated active

Operation period (yrs) 21 31 28 36

Fill area (ha) 3.7 12.2 40.6 21.2

Maximum fill height (m) 12 (24) 1 20 (8) ~

Special wastes codisposed metal sludges metal sludge,oils metals,solvents metals,so/vents,ash etc.

Covering during use (X) z (X) z X X

Compaction during use (X) X X

Final cover X (X) z X

Landscaping vegetation grass grass grass, willow (part)

Distance to housing (m) 250 150 100 100 (2800) 3

'Ettala (1988); ZPartial or uncertain; 3Distance to urban inhabitation in parentheses.

i

f FINLAND \ • S U L K A V U O R I

1 0 SO 100kin _ ~ I I I

' ~ " ~ ' ' - - D O M A R G , ~ R D I b _ , ' , . J ' - - " ~ J " " '

21 o 20 °

I 1 Fig. 1. Location of the study sites.

1 2 0 9

Sampling and field measurements

Sampling structures mainly consisted of ca. 110 mm PVC wells or 30-50 mm piezometers, inserted in the fills either

in excavated trial pits, or by augering or drilling and sealed with lids and compacted soil.

Gas sampling was conducted in late spring and early autumn 1989-90. Samples were taken either through direct

reading instruments or electric suction pumps (SKC R Co.) equipped with Teflon TM piping (Fig. 2). Gas was withdrawn

before sampling until oxygen-free (as checked by Crowcon TM Tri-X field instrument) to improve the representativeness

of the samples. The calibrated gas flow rate for the laboratory samples was usually 455 ml/min.

The samples were collected in baked steel tubes flushed with pure air and filled with Tenax TM (Harkov et al. 1985,

NIOSH 1988). The tubes were capped with steel lids and stored (:old and dark until analysis. The integrity of test

samples in +4°C and -20°C was ascertained with successive analyses; refrigeration was found to be sufficient.

Duplicate samples were collected immediately after each other for all laboratory analyses. Field blanks were otherwise

trealed as the other tubes but excluding landfill gas. Before sampling, the equipment was flushed with sample gas to

reduce cross-contamination, especially between each study site (Kak:vi 1991).

Analytical methods

Field measurements were made of key trace gases (benzene, toluene) using screening colorimetric Dr~iger TM tubes

(Fig. 2) with variable measurement principles, specificities and sensitivities; typical reported detection limits are 5 ppm.

The laboratory analyses were mainly carried out at the Institute lbr Occupational Health district laboratories after

thermodesorption using capillary gas chromatography with flame ionization detection (Kalevi 1991). The detection limits

varied depending especially on the substances. Average recoveries were estimated on the basis of standard compounds,

and the sample concentrations were calculated with recovery factors, accounting for eventual breakthrough.

Fig. 2. Sampling equipment and techniques.

1 2 1 0

RESULTS AND DISCUSSION

Occurrence and concentrations of trace compounds

Chlo r ina t ed m e t h a n e s were among the dominant organic trace compounds of those analyzed (Table 2). They have

been widely used also in Finland in industrial and other wastes, particularly as solvents,

Table 2. Coqcentrations (mg/m 3) of trace organic contaminants measured in gas samples from the various municipal

landfills ( 1989 -90 data).

Compound St u d y s i l e

Domargfird ~ Mankkaa Sulkavuor[ Kujala

Min x Max n Min x Max n Min x Max n Min x Max n

llalo~enated aliphatic hydrocarbon~

DCM 0.8 1.0 1.5 3 1.0 47.5 112 8 84 18 36 4 21 30 42 4

CtlCI 3 "~ 2.8 3.2 3.9 3 7.0 34.7 62 8 7 9 10 15 4 38 54 70 4

CCI, 3 1.4 1.7 2.2 3 0.9 34.3 88 8 68 9 11 4 12 27 42 4

12-DCEa <0.1 0.3 0.6 3 <0.1 0.95 2 8 <0.1 0.2 0.7 4 0.3 0.7 1.6 4

l l l -TCEa x 0.5 0.6 0.8 3 0.3 8.5 21 8 2.4 3.0 3,9 4 4.1 9.5 15 4

l l2-TCEa <0,01 0.6 1.8 3 <0.01 2.0 3 8 0.26 0.33 0,52 4 8.2 8.7 9.3 4

l122-TeCEa <0.4 <0.4 <0.4 3 <0.4 0.7 1 8 <0.4 <0.4 <0.4 4 <0.4 0.4 0.5 4

t-12-DCEe 2.8 3.1 3.5 3 1.3 19.5 41 8 6.0 8.0 9.9 4 23 30 37 4

TCEe <0.1 <0.1 <0.1 3 <1.0 5.25 13 8 2.6 3.3 4.6 4 <1.0 2.0 3.7 4

TeCEe 2 0.9 1.3 2.1 3 <0.1 26.9 50 8 4.5 6.4 9.0 4 34 47 62 4

EtDBr ' <0.5 1.9 2.7 3 <0.5 5.65 16 8 <0.5 <0.5 <0.5 4 <0.5 0.5 0.5 4

FREONll3 2.7 3.2 4.0 3 1.3 4.5 12 4 4.7 7.6 14 4 39 44 49 4

Aromatic hydrocarbons and phenolic cc.mpound~

Benzene 8 9 11 3 <0.1 1.4 5 10 0.3 1.4 2.9 4 3.6 3.9 4.2 4

Toluene 0.2 0.23 0.3 3 9 58.5 139 10 0.2 0.5 0.7 4 133 137 143 4

o-Xylene <0.1 0.6 0.9 3 <0.1 1.9 3.4 10 <0 1 0.1 0.2 4 33 35 36 4

m-Xylene 3.0 3.4 3.8 3 <0.1 7.4 12 10 <01 0.2 0.3 4 115 125 130 4

p-Xylene <0.1 1.0 1.5 3 <0.1 2.8 5.0 10 <0.1 0.2 0.3 4 40 42 44 4

l-thylbenzene 6.6 7.0 7.6 3 <0,1 6.7 9.6 10 0.2 0.6 1.2 4 85 89 98 4

Styrene ' <0.1 0.3 0.4 3 <0.1 0.8 2.0 10 <0.1 <0.1 <0.1 4 <0.1 0.1 0.1 4

o-Cresol <0.01 <0.01 <0.01 3 <0.01 <0.01 <0.01 6 <0.01 <0.01 <0,01 4 <0.01 <0.01 <0.01 4

m-Cresol <0.01 <0.01 <0.01 3 <0.01 <0.01 <0.01 6 <0,01 <0.01 <0,01 4 <0.01 <0.01 <0.01 4

p-Cresol <0.01 <0.01 <0.01 3 <0.01 <0.01 <0.01 6 <0.01 <0.01 <0,01 4 <0.01 <0.01 <0.01 4

l lalogenated benzenes

MCBz 0.02 0.02 0.02 3 <0.01 0.1 0.2 8 <0.01 0.09 0.32 4 0.07 0.19 0.33 4

12-DCBz <0.01 0.03 0.04 3 <0.01 0.2 0.4 8 <0.01 <0.01 <0.01 4 0.09 0.10 0.13 4

13-DCBz <0.01 0.02 0.03 3 <0.01 0.17 0.3 8 <0.01 <0.01 <0.01 4 <0.01 <0.01 <0.01 4

14-DCBz <0.05 <0.05 <0.05 3 <0.05 0.18 0.3 8 <0.05 <0.05 <0.05 4 <0.05 <0.05 <0.05 4

123-TCBz <0.01 0.01 0.03 3 <0.01 <0.01 <0.01 4 <0.01 <0.01 <0.01 4 <0.01 <0.01 <0.01 4

124-TCBz <0.05 <0.05 <0.05 3 <0.05 <0.05 <0.05 4 <0.05 0.07 0.13 4 <0.05 0.06 0.11 4

1234-TeCBz <0.01 <0.01 <0.01 3 <0.01 <0.01 <0.01 4 <0.01 <0.01 <0.01 4 <0.01 <0.01 <0.01 4

PCBz <0.01 0.01 0.02 3 <0.01 <0.01 <0.01 4 <0.01 <0.01 <0.01 4 <0.01 <0.01 <0.01 4

llCl:~z <001 <0.01 <0.01 3 <0.01 <0.01 <0.01 4 <0.01 <0.01 <001 4 <001 <0.01 <001..z:'L

'Minimum values due to potential sample breakthrough; zaa"Assuming the presence at a time of only the other one in a compound

pair, nol diffcrentiable by chromatography.

i 2 1 1

The observed concentration ranges and averages are in the same order of magnitude as in many other studies of

landfill gas and well above background levels (Table 3). However, comparisons are difficult due to varying

methods of sampling and analysis. This may also contribute to the considerable differences in concentrations

observed between our data and those reported by Ettala (1988) on the basis of bag samples, in part from the same

landfills.

Some chlorinated ethenes, notably t-l ,2-dichloroetehen and tetrachloroethene, were rather frequently found in

concentrations considerably exceeding background values. They have been found in correspondign concentrations

also in many other landfill gas studies (Table 3). Interestingly, tetrachloroethylene was not commonly present in

leachatcs from these landfills, which may be due to its preferential volatilization as well as decomposition in the

fills (Assmuth et al. 1990). Among its decomposition products, vinyl chloride may poses airborne hazards (Wood

& Porter 1987).

Of chlorof luorohydrocarbons only FREON 113 was analyzed and occasionally found in high concentrations.

Since CFC compounds are not effectively retained in Tenax, its concentrations have evidently been even higher.

Baccini et al. (1987) have shown the significance of gaseous fluorine emissions, but did not elucidate what specific

substances they contain. Scott et al. (1988) have found AOF concentrations of up to 200 mg./m 3 especially in fl-esh

landfill gas. Others have measured high concentrations of several common CFC compunds in landfill gas (e.g.,

Rettenberger 1987).

Several aromatic unhalogenated hydrocarbons were commonly found in significantly elevated concentrations,

especially the 'BTEX compounds' toluene, xylenes, ethylbenzene and benzene. These w)latile substances have also

been among the dominant organic trace compounds in many other hmdfill gas studies, and include toxicologically

significant substances (Table 3).

Chlorobenzenes were not detectable, except for occasional mono- and dichlorobenzene occurrence. This is

logical, considering the relatively small volatility of especially highly chlorinated forms. Of phenolic compounds,

cresols were analyzed. Their concentrations were consistently below detection levels.

Variations in gas concentrations

Frequency distributions of the a,lalyzed trace compounds were in some cases non-normal (negatively skewed)

and truncated due to frequent values below detection limits (Table 2). Also other landfill gas investigators have

observed non-normally and no,l-lognormally distributed concentrations (Ettala 1988) and resultant maxima in

excess of (geometric) means (Harkov et al. 1985). However, these distribution features in our data were not st)

common or clear as with contaminaqts in solid or liquid phases (Assmuth et al. 1990, 1991).

Variation in concentrations between the sites was observed with several compounds. There are many factors

potentially causing variation, including the effect of sample representativity. The differences between the study

sites may in part be due to the age of the landfill (cf. Rettenberger & Stegmalm 1991) but also to differences in the

ofigi,~al presence, as a consequence of disposal, of these compounds in the studied fills. E.g. the Kujala landfill,

exhibiting high concentrations of many volatile hydrocarbons, is known to have received considerable amounts of

solvents in co-disposal of industrial wastes.

Variation between duplicate samples, as a result of measurement system variability, was usually rather small

(Fig. 3). Much greatcr sources of variability are likely to be caused by the rcpresentativity of sampling. Conse-

quently, on the basis of this preliminary study stage the average concentrations in gas fluxes over extended areas

or periods cannot be efficiently quantified. Such variations are presently subject to further investigations.

Covariation in contami,mnt concemrafions was observed between many of the abundant trace compounds,

especially chlorinated methanes and ethanes/ethenes i,1 the pooled data, as is illustrated by the highly significant

linear correlations of their concentrations (Fig. 3).

1 2 1 2

10(3 10( - ---

60 I 63 I

20 2 C

i 10 • •

i i J t p

111 - Tr i c h l o r o e l h a n e D l c h l o r o m e l h o n e

Figure 3. Scatter and covariation of the concentrations of common ch]onnated contaminants in laudfill gas.

Values from duplicate measurements are connected. Note the variable logarithmic scales and resultant linear

regression curves (based on means of duplicates). One of the points in the left figure is not shown.

Table 3. Summary statistics of the concentrations of key contaminants (mg/m 3) measured in gases in municipal

solid or mixed waste landfills, and reference values.

Substance(s) This study Other studies Urban Occupat. LOEL, VDI Car-

air, air quality animal norm, cino-

x max. Finland ~ UK/G/USA ~ Turku/ norms 4 inhal, plants genic

xM~ 8 Range Hamburg 3 s ~ ,

Dichloromethane 1.0-47.5 112 <0.1-190 350 1765 20

Chloroform 3.2-54 70 0.056 <0.01-0.8 50 249 +

Carbon tetrachloride 1.7-34.3 88 0.33 14 20 3 +

12-Dichloroethane 0.2-0.95 2 <0.1-8 <0.119 4.5 5000 8 +

111-TdchIoroethane 0.6-9.5 21 0.59 <0.1-177 <0.043 540 30

112-Trichloroethane 0.3-8.7 9.3 <0.0001 45 2780 +

1122-Tetrachloroethane <0.4-0.7 1.0 0.033 <0.0006 7 6980 +

t-12-Dichloroethene 2.2-30 41 <0.1-302 790 4800

Trichloroethene <0.1-5.3 13 2.8 <0.1-170 <0.018 160 30

Tetrachloroethene 1.3-47 62 1.6 <0.1-350 <0.071 185 660 +

Ethylenedibromide <0.5-7.8 16 145 3090 35

Benzene 0.17-9 11 0.4-180 <0.019 3.5 65 3 +

Toluene 0.23-137 143 8-460 <0.058 375 350 20

Ethylbenzene 0.60-89 98 17-330 <0.022 435

Styrene <0.1-1.1 2.0 <0.1-7 85 2600

Chlorobenzene 0.01-0.19 0.33 <0.1-2.1 230 936 5

~Ettala 1988; 2Brookes & Young 1983, Young & Parker 1983, Young & Blakey 1991 / Bruckmann & Miilder 1982,

Janson 1988, Rettenberger & Stegmann 1991 / Wood & Porter 1987; 3Kroneld 1989 / Bruckmann et al. 1988;

'Lowest of Finnish or American Occupational Safety and Health Administration; SLowest reported (acutely) toxic

inhalatory level (for mammals), Lewis & Sweet 1984, Nikunen et at. 1990; ~Maximum advisable Iongterm immission

concentration for plants, VDI 1990; 7Nikunen et al. 1990; SGreatest of site averages.

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Environmental significance of trace gases

Concentrations and toxicity

Occupational air quality norm violations by the concentrations of the analyzed contaminants occurred relatively

seldom, mainly by carbon tetrachloride (Table 3). The norms vary (e.g., Kalevi 1991) and are generally becoming

stricter, due in part to increasing information on sublethal and chronic health effects, e.g. associated with various

target organs and synergism, not yet wholly reflected in norms (Scott et al. 1988, Baldwin & Scott 1991).

Of particular concern are the landfill gas components known or suspected to be carcinogenic. These include

chloroethanes, -ethanes and -ethenes as well as benzene, for which human carcinogenicity has long been evident.

Also DCM belongs to these compounds of potentially strong chronic (geno)toxicity. However, no numerical values

of cancer potency corresponding e.g. to the oral TDso (tumorigenic doses) are available for inhalation exposures.

Moreover, occupational air quality norms are not directly applicable to the assessment of ecotoxicological and

other environmental effects. For a more comprehensive assessment of the observed trace compounds in landfill gas,

various effects and organisms, as well as associations of organisms, have to be considered (Table 3). However,

relevant toxicological data are sparse. Among ecotoxicological effects, damage and inhibition of plants or of the

methanogenic and other microflora operative in the decomposition of landfilled waste may occur (Poller 1991).

Several volatile toxic substances not analyzed in this study have been found to be frequently present in landfill

gas exceeding threshold limit values, including other chlorofluorohydrocarbons, alcohols and sulphur compounds,

especially the highly odorous methanethiol (Brookes & Young 1983, Young and Parker 1983, Scott et al. 1988).

Also alkanes and esters reached considerable concentrations (Brookes & Young 1983, Rettenberger 1987). Among

the rarely analyzed gas constituents, the impacts of toxic nitrogen compounds and organometals, e.g. mercury fluxes

(Bergvall et al. 1988), are noteworthy.

The environmental significance of the emitted compounds is dependant on many factors affecting their

subsequent migration and fate (Thibodeaux 1981, Baker & MacKay 1985, Harkov et al. 1985, Stephens et al.

1985, Wood & Porter 1987, Karimi et al. 1988). Most gases undergo rapid dilution outside the fills, but those

migrating at or under the soil surface, or attached on aerosols, may reach vulnerable targets in higher concentra-

tions. Crucial factors determining the fate and impacts include degradability, contributing to the importance of

persistent compounds such as Freons, bioaccumulation and the properties of transformation products, e.g. the car-

cinogenicity of vinyl chloride.

The concentrations of many contaminants commonly exceeded background levels in urban ambient air,

maximally by a factor of ca. 100 000 as compared with literature values, reflecting dilution effects and potentially

other attenuation mechanisms. The observed concentrations were orders of magnitude higher than those measured

in the crawling space of buildings adjacent to Dutch sites with heavy soil contamination (Fast et al. 1988).

Emission estimates

Quantitative estimates of gas fluxes from landfills are constrained by the lack of representative data on gas

concentrations and flows. The emission estimates for the dominant trace compounds from Finnish landfills, based

o,1 observed average concentrations and on estimated cumulative gas generation rates at Finnish field-scale

utilization schemes of ca. 70 m3/t waste (Ekono Ltd. 1987), are of the order of kg/d (t/yr). Some American

estimates of the total landfill emissions of benzene, chloroform and vinyl chloride are much higher (up to 10 ~

kg/yr), but involve several assumptions, many of them conservative. Measurement-based estimates have been much

smaller, generally some hundreds of kilograms/yr (Wolfinger 1987).

The emissions of the predominant trace gases from the study sites seem substantially larger than the respective

waterborne emissions (Assmuth et al. 1991), as may be expected on the basis of their solubility and volatility. For

1214

fluorine the same order of significance of these emission routes was found by Baccini et al. (1987); fluorine has

been estimated to originate predominantly from CFC compounds, whose relative share of fluxes increases due to

the large amount disposed and the control of other sources (Laugwitz et al. 1990).

The uncertain obtained estimates of landfill emissions seem generally smaller than those of e.g. industrial use

of solvents (Mroueh & Laukkarinen 1985, Mroueh 1988, Nyquist 1986, Wallace 1990). In addition to the present

emission rate, the total storage in landfills and the period of release are important, and may imply a rise in the

relative significance of landfills in relation to other sources.

Of the main gas components, methane poses particular environmental hazards due to its explosivity and high

potency as a greenhouse gas. The CH 4 emissions from landfills have been estimated to be ca. 10 % of total

(anthropogenic) emissions, and are among the sources amenable to control (e.g., Salmikangas & Laukkarinen 1990,

Rettenberger & Stegmann 1991, Thomeloe 1991).

The quantitative importance of non-gaseous air emissions from landfills is poorly understood. Many important

nonvolatile organic compounds may migrate on landfill dust particles. The emissions of toxic organic compounds,

e.g. PCDD's, in landfill fires are potentially significant, as observed experimentally Persson & Bergst6m 1991).

CONCLUSIONS

1. Several harmful trace organic compounds were found in gas samples from municipal mixed waste landfills in

concentrations well above background values, especially chloromethanes and volatile aromatic (BTEX)

compounds.

2. Variation was observed between the sites in volatile organic hydrocarbon concentrations, reflecting differences

in both waste contents and site conditions. Concentration distributions were rather normal as compared with e.g.

those in waste or leachate.

3. Of the compounds analyzed in this study, those estimated to pose the most severe toxicological risks due to

their concentrations and acute toxicities or carcinogenicity included carbon tetrachloride, dichloromethane,

toluene and benzene.

4. The rough estimates of the emissions of the dominant trace gases analyzed, based on concentration data and gas

generation figures from other landfills, were of the order of kg/d, exceeding the respective waterborne fluxes,

but probably minor in comparison with other air emissions.

5. The sampling and analytical methods employed seemed generally suitable for measurement of trace compounds

in landfill gas. For a more comprehensive assessment of their significance, further developments and extensions

~re needed in field measurements and in quantitative information on contaminant fate and effects.

ACKNOWLEDGEMENTS

The contributions of fellow researchers Ms. Helena Poutanen and Mr. Tapio Strandberg is gratefully acknowled- ged, as is the assistance of several other persons within and outside the Water and Environment Administration, particularly at the Finnish National Institute of Occupational Health laboratories. This research has been funded primarily by the Ministry of the Environments. The views expressed are those of the authors alone.

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( R e c e i v e d i n G e r m a n y 4 J a n u a r y 1 9 9 2 ; a c c e p L e d :t9 F e b r ~ u a r y 1 9 9 2 )