Effects of Sewage Sludges Contaminated with Polychlorinated

of the sewage sludge on the soil. The values of sludge- treated areas were compared with the limits proposed in. Germany for agricultural and horticul...
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Environ. Sci. Technol. 1997, 31, 2765-2771

Effects of Sewage Sludges Contaminated with Polychlorinated Dibenzo-p-dioxins, Dibenzofurans, and Biphenyls on Agricultural Soils ETHEL ELJARRAT, JOSEP CAIXACH, AND JOSEP RIVERA* Mass Spectrometry Laboratory, Ecotechnologies Department, C.I.D., C.S.I.C., Jordi Girona 18-26, 08034 Barcelona, Spain

The fate of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) in sewage sludges after agricultural application was analyzed. This study was based on the experiments designed for two soils with different agronomical characteristics after applying different rates of sewage sludge. The concentrations of PCDDs, PCDFs, and PCBs in soils were determined before and after the application of sewage sludges, and a general increase was observed with the applied rate, especially in the case of the PCDDs. The values of sludge-treated areas were 1.2-11.6 times higher than the respective values of the noncontaminated areas. Changes observed in the ratio between PCDD and PCDF levels and in the isomeric distribution also suggest the influence of the sewage sludge on the soil. The values of sludgetreated areas were compared with the limits proposed in Germany for agricultural and horticultural land uses. The results of the soil investigation showed that, in the case of an initial soil with low contamination, the final soil did not exceed the limit; but, in the case of an initial soil with considerable contamination, the final soil exceed the limit, which restricts the cultivation of certain vegetables.

Introduction A number of different directives concerning wastewater sewage sludges have been issued in the last decade. For instance, the promulgation of the Directive COM 91/271 on wastewater treatment requires the installation of treatment systems in all populations exceeding 2000 inhabitants before the year 2005 (1). Estimates for the year 2000 predict an increase in sewage sludge production of 185% in Spain, which means about 1 milion ton/year. On the other hand, the effect of some new directives on treatment and elimination of toxic and dangerous wastes, the EU Directive on agricultural use of sludges (COM 86/278) (2), and the banning of sewage sludge discharges into the sea from 1998 (1) all combine to restrict the final fate of sewage sludges. However, by the end of the millenium, there will be much more sludge and further restrictive environmental laws on their use and disposal. The application of sewage sludge to land is a widely practiced sludge management technique. In many countries there is a continuous discussion on the significance of sewage sludge fertilization of cultivated land in terms of soil contamination. In recent years, the recognition that sewage sludge contains organic pollutants, in particular PCDDs, PCDFs, and PCBs (3-8), has resulted in studies to identify the possible sources of these contaminants in sewage sludge and to assess the extent to which they may be transferred through the food chain and ultimately to humans. PCDDs

S0013-936X(96)01060-7 CCC: $14.00

 1997 American Chemical Society

and PCDFs in the sewage sludges may be attributed to different sources as (a) atmospheric deposition (9); (b) transformation of chlorinated organic precursors such as chlorophenols during treatment at wastewater plant (1012); (c) industrial dumps from textile, metal, pulp, and paper factories (13); (d) domestic wastewater (13); etc. The application of sewage sludges to soils is limited by guideline concentrations of heavy metals in the soil through the EU Directive on the use of sewage sludge in agriculture (COM 86/278) (2). No similar guidelines exist for organic contaminants in sludges or soils at present. The European Union is currently studying the issue and may enact legislation on the application of sewage sludges containing PCDDs, PCDFs, and PCBs to agricultural land. However, in Germany in 1992, the Ordinance on Sewage Sludge (14) established a limit of 100 pg of I-TEQ/g of sludge (dry weight, dw) for PCDDs and PCDFs and 200 ng/g of sludge (dw) for the six PCBs congeners (28, 52, 101, 138, 153, and 180) for agricultural purposes. Furthermore, this regulation set an application limit of 5 ton/ha within a period of 3 years. The purpose of this study was to assess the effects of PCDDs, PCDFs, and PCBs in sewage sludges applied to the soil. The work was based on an experiment devised during the 1980s. Two doses of sewage sludges were applied to two different soils for 4 consecutive years. The characterization of these soils before the experiment and after the application shows the fate of these contaminants from sewage sludge to the soil.

Experimental Section Design of Experiment. The samples used in this experiment are summarized in Table 1. Two different plots of land were selected for this study. Every plot was divided into 4 × 4 squares with subplots of 8 × 5 m2. In the first plot, located in Caldes de Montbui (NE Spain), the soil was agronomically satisfactory, with a sandy loam texture, a basic pH, and an adequate organic matter content. This soil was characterized as a Xerochrept by the STS (Soil Taxonomy System). By contrast, in the second one, located in Tordera (NE Spain), the soil had a sandy texture, a slightly acid pH, and a poor nutrient and organic matter content, which indicates an agronomically deficient soil. Raygrass (Lolium westerwoldicum var. Balwoltra) was planted as an annual on irrigated land. This variety was chosen given its high nutrient requirements for growing; for this reason, we were able to apply high levels of sewage sludges and hence determine the effects produced in a shorter period of time. The applied sewage sludges were collected from the wastewater treatment plants located in the villages of Tossa, Figueres, and Roses (NE Spain). These plants treat sewage sludges, which are mainly of urban origin, aerobically. A small industrial input exists at the Figueres plant, and a leisure boat marina input exists at the Roses plant. Two different rates of sewage sludges, a “low” dosis and a “high” doses (double the low doses), were applied. The application rates are summarized in Table 1. The differences between the amounts applied are due to the different characteristics and properties of each sewage sludge. The doses were calculated on the basis that approximately 20% of the total nitrogen present in the sewage sludge was mineralized in one agricultural cycle for the low dosis, and approximately 40% of the total nitrogen was mineralized for the high dosis. Thus, the sewage sludge with the highest nitrogen content required smaller rates of application. The doses commonly applied in spanish agriculture are much lower, ranging between 5 and 10 ton (dw) ha-1 year-1.

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TABLE 1. Summary of Chemical and Physical Properties of Soil and Sewage Sludge Samples ton (dw)/ha sample

ref

pH

% OMa

initial soil sludge applied in 1983 sludge applied in 1984 sludge applied in 1985 sludge applied in 1986 final soil (low dose) final soil (high dose)

BIS BSS83 BSS84 BSS85d BSS86 BFS(L) BFS(H)

8.24 6.20 6.65 6.55 6.67 7.68 7.24

2.34 70.35 54.43 48.92 51.53 3.46 4.14

initial soil sludge applied in 1982 sludge applied in 1983 sludge applied in 1984 sludge applied in 1985 final soil (low dose) final soil (high dose)

AIS ASS82 ASS83 ASS84 ASS85 AFS(L) AFS(H)

6.84 6.42 6.68 6.55 6.55 6.53 6.15

1.11 54.62 62.87 39.08 48.92 3.15 3.36

a

OM, organic matter, expressed in dry weight.

b

%N

9

densityb

low dose

high dose

Experiment in Basic Soil 0.13 4.85 50.0 3.75 9.4 3.69 11.2 3.55 4.3 0.20 1.53 0.25 1.42

22.00 32.25 25.00 29.87

44.00 64.50 50.00 59.75

Experiment in Acid Soil 0.06 4.44 40.9 4.85 41.7 2.84 5.5 3.69 11.2 0.17 1.45 0.23 1.35

37.29 21.94 32.15 26.31

74.60 43.87 64.30 52.62

Humidity. c Density expressed in g/cm3.

Superficial layers (20 cm) of soil samples were collected in a deeper stainless steel corer. Final soil samples were taken 1 year after the last sewage sludge application. All the samples (soils and sewage sludges) were collected, air-dried, and kept in glass storage containers by the Escola Superior d’Agricultura of Barcelona during the 1980s. The experiment was used to quantify the inputs of metals (Zn, Cu, Ni, Pb, Cr, and Cd) to agricultural soils in sewage sludge and to investigate their fate and effects on the soil (15). After these analyses, samples were stored in sealed containers in the darkness. Before storage, the percent of humidity was determined by heating at 105 °C until constant weight, and the percent of organic matter was determined by Walkley-Black method. Today, the archived samples were used to assess the effects of organic compounds such as PCDDs, PCDFs, and PCBs. Extraction and Cleanup. The samples were manually ground before extraction. Ten-gram (dw) sludge samples and 30-g (dw) soil samples were spiked with a mixture of 15 13C -labeled 2378-substituted isomers (Chemsyn Science 12 Laboratories, Lenexa, USA) and extracted in a Soxhlet apparatus for 48 h with toluene of pesticide grade (Merck). No internal standard was used for PCB analyses. Five gram of copper was added to the Soxhlet beaker to remove sulfur interferences. In order to avoid possible combination chemistry at temperature higher than 100 °C between halogenated aromatic species present in the crude extract and native copper metal, this one was added in the beaker where the temperature was similar to room temperature. After extraction, crude extracts were transferred to hexane and treated with concentrated H2SO4, followed by purification via a three-stage open column chromatographic procedure (16). Column A contained, from top to bottom, layers of Na2SO4, silica gel, H2SO4-impregnated silica, silica gel, NaOHimpregnated silica, silica gel, and AgNO3-impregnated silica. The column was eluted with hexane and concentrated before application to column B, which was packed with Florisil (activated overnight at 600 °C). Elution of column B with (a) hexane and (b) toluene/diethyl ether (9:1) yielded two fractions, one containing the PCBs and the other containing the PCDDs/PCDFs. The latter fraction was concentrated before application to column C, which was packed with basic alumina (activated overnight at 300 °C). Elution with hexane, hexane/CH2Cl2 (2%), and hexane/CH2Cl2 (50%) yielded the PCDDs/PCDFs in the third fraction. Samples were finally concentrated to incipient dryness prior to the addition of a mixture of 13C12-labeled 1234-TCDD and 13C12-labeled 123789HxCDD as the recovery standard (16).

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d

location Caldes de Montbui Tossa Figueres Figueres Figueres Caldes de Montbui Caldes de Montbui Tordera Roses Roses Figueres Figueres Tordera Tordera

BSS85 ) ASS85.

Instrumental Analysis. Purified PCDD/PCDF extracts were analyzed by HRGC-HRMS on a Fisons 8060 gas chromatograph fitted with a DB-5 (J&W Scientific, CA, USA) fused-silica capillary column (60 m × 0.25 mm i.d., 0.25 µm film thickness) coupled to an AutoSpec-Ultima (VG, Manchester, UK) mass spectrometer operating in the electron impact ionization (electron energy 38 eV) at 10.000 resolving power. Chromatographic separation of components was achieved as follows: from 140 °C (for 1 min) to 200 °C at 20 °C/min (held isothermally for 1 min) and then to 300 °C (maintained for 20 min) at 3 °C/min. The carrier gas was helium at a pressure of 175 kPa. The injector temperature was 280 °C, and the injection mode was splitless for 60 s. Quantitative determination was performed by the isotope dilution method using relative response factors (RRFs) previously obtained from five standard solutions (CSL, Lenexa, USA) (17). The 15 labeled PCDD and PCDF internal standards and respective RRFs were used for quantitation of unlabeled PCDDs and PCDFs and for determination of method detection limits. For example, the [13C]2378-TCDD was used to quantify the 2378-TCDD isomer, and all other TCDD isomers present. [13C]OCDD was used in a similar manner for OCDD and OCDF. The data achieved were evaluated using defined analytical criteria and requeriments. The acceptance criteria for data include acceptable chlorine isotope ratios, retention time, and signal-to-noise ratio. Purified PCB extracts were analyzed by HRGC-ECD on a KNK-3000 gas chromatograph (Konik, Barcelona, Spain) equipped with a Tracor (Austin, TX) electron-capture detector using nitrogen as the makeup gas. A DB-5 (J&W Scientific, CA, USA) fused-silica capillary column (60 m × 0.25 mm i.d., 0.25 µm film thickness) was used with hydrogen as the carrier gas. The temperature program was from 70 °C (held for 0.7 min) at 20 °C/min to 150 °C (held isothermally for 1 min) and then to 280 °C (maintained for 15 min) at 4 °C/min; the injector and detector temperatures were 250 and 310 °C respectively. The injection mode was splitless for 45 s. The chromatographic data were processed using a Merck-Hitachi D-2000 integrator. The compounds were assigned according to their retention times as compared with standard mixtures; quantification was done by comparing with Aroclor 1260 and with a mixture standard of PCB congeners 28, 52, 101, 118, 153, 138, and 180 (Cromlab, Barcelona, Spain). These seven PCB congeners have been described by Ballschmiter (18) as BCR (Community Bureau of Reference) congeners.

TABLE 2. Concentrations of PCDDs, PCDFs, and PCBs (Expressed in Dry Weight) in Seven Sewage Sludge Samples Applied to Different Soils Studied BSS83

BSS84

BSS85 ) ASS85

BSS86

ASS82

ASS83

ASS84

2378-TCDD 12378-PeCDD 123478-HxCDD 123678-HxCDD 123789-HxCDD 1234678-HpCDD OCDD 2378-TCDF 12378-PeCDF 23478-PeCDF 123478-HxCDF 123678-HxCDF 234678-HxCDF 123789-HxCDF 1234678-HpCDF 1234789-HpCDF OCDF

0.6 4.2 3.8 6.8 E01 4.0 E01 3.4 E03 1.6 E04 2.5 E01 1.1 5.2 1.7 E01 4.7 9.6 NQa 1.0 E02 3.2 9.4 E01

Results Expressed in pg/g (dw) 1.0 0.1 0.8 9.0 9.5 6.1 2.6 E01 1.0 E01 9.2 3.3 E02 2.1 E02 2.5 E02 1.3 E02 9.1 E01 5.3 E01 1.2 E04 6.4 E03 1.5 E04 4.3 E04 2.6 E04 4.9 E04 7.8 E01 6.0 E01 4.7 E01 1.3 E01 8.8 3.5 2.7 E01 2.0 E01 7.9 4.6 E01 2.8 E01 1.5 E01 2.7 E01 1.7 E01 7.3 3.9 E01 2.1 E01 1.0 E01 1.5 NQ 0.3 5.5 E02 1.7 E02 1.7 E02 2.8 E01 1.0 E01 9.1 6.1 E02 2.4 E02 4.0 E02

0.7 3.8 1.2 E01 1.7 E02 9.1 E01 5.0 E03 1.8 E04 1.9 E01 2.9 4.1 1.8 E01 6.1 1.1 E01 0.2 7.8 E01 2.8 7.7 E01

0.1 3.5 4.0 4.7 E01 2.8 E01 1.7 E03 1.9 E04 2.8 E01 4.0 6.3 1.3 E01 5.8 8.7 0.1 1.2 E02 6.0 1.6 E02

1.9 8.3 7.1 1.0 E02 5.3 E01 4.5 E03 2.1 E04 4.3 E01 1.5 E01 1.6 E01 2.4 E01 1.2 E01 1.5 E01 NQ 1.0 E02 6.3 1.9 E02

PCB 28 PCB 52 PCB 101 PCB 118 PCB 153 PCB 138 PCB 180 total PCBs

4.2 1.4 E01 1.6 E01 2.2 E01 2.2 E01 2.4 E01 1.7 E01 5.3 E02

Results Expressed in ng/g (dw) 1.4 4.4 1.3 E01 5.4 7.8 1.0 E01 5.3 5.1 5.9 7.0 7.9 7.3 7.0 4.1 1.2 E01 8.5 4.1 1.2 E01 3.2 1.9 7.2 2.2 E02 1.9 E02 2.8 E02

3.4 5.2 4.1 6.7 1.2 E01 1.1 E01 1.0 E01 2.1 E02

6.5 1.3 E01 1.1 E01 1.9 E01 2.2 E01 2.1 E01 1.5 E01 4.4 E02

7.2 1.3 E01 1.2 E01 1.8 E01 2.1 E01 2.2 E01 1.3 E01 5.0 E02

total PCDDs total PCDFs R(I-TEQ PCDDs/I-TEQ PCDFs) total PCDDs + PCDFs

6.4 E01 9.5 6.8 7.4 E01

Results Expressed in pg of I-TEQ/g (dw) 2.2 E02 1.2 E02 2.4 E02 3.9 E01 2.5 E01 1.4 E01 5.5 5.0 16.5 2.6 E02 1.5 E02 2.5 E02

9.8 E01 8.5 11.5 1.1 E02

4.6 E01 1.0 E01 4.4 5.6 E01

8.8 E01 1.9 E01 4.6 1.1 E02

a

NQ, not quantified (Rs/n < 3).

Results and Discussion Sewage Sludges Investigation. The concentrations of PCBs and the tetra- through octa-CDD/F congeners and homolog groups in the seven sewage sludges analyzed are given in Table 2. All of the 2378-substituted isomers and the seven BCR congeners of PCBs were detected in the seven samples analyzed, with concentrations at the picogram and nanogram per gram level, respectively. A general increase in concentration with chlorination can be observed, the predominant congener being OCDD. This is consistent with reported data for sewage sludges (5,19-23). Dioxin and furan recoveries values, ranging from 84 to 104%, revealed a satisfactory analysis procedure. To normalize concentrations and toxicity of the various PCDD and PCDF congeners, international toxicity equivalent factors (I-TEFs) (24) were used to calculate international toxicity equivalent (I-TEQ) for the samples. The I-TEQ values represent the equivalent concentration of 2378-TCDD. In 1992, a limit value of 100 pg of I-TEQ/g of dry matter for PCDDs/PCDFs and 200 ng/g for PCBs in sludges used in German agriculture was established (14). From the seven samples analyzed, five clearly exceeded this limit (1.1 E02, 1.1 E02, 1.5 E02, 2.5 E02, and 2.6 E02 pg of I-TEQ/g). The variation in the I-TEQ concentration can be explained because the different sewage treatment works were exposed to varying loads during the sample collection period. The concentrations of the sum of PCDD were higher than those of the sum of PCDF, with the ratio R(I-TEQ PCDDs/I-TEQ PCDFs) > 1, and the values ranged between 4 and 17, which matched reasonably well those observed by Rappe et al. (25). The TEQ values of these archived samples were higher than those measured in the contemporary sludges, which presented levels ranging from 13 and 41 pg of I-TEQ/g (data unpublished). This may

reflect a general decline in PCDDs/PCDFs inputs to the environment due to tighter controls on organochlorine use and disposal. Regarding the PCBs, the levels ranged from 1.9 E02 to 5.3 E02 ng/g on an Aroclor 1260 basis, and the sum of the PCBs 28, 52, 101, 138, 153, and 180 ranged between 27 and 98 ng/g, always below the limit set for 200 ng/g. These six congeners were found in the following order of abundance: 153 > 138 > 180 > 52 > 101 > 28. Soils Investigation. The concentrations of PCBs and the tetra- octa-CDD/F congeners and homolog groups in the six soils analyzed are given in Table 3. The most toxic isomer, the 2378-TCDD, could only be quantified in one sample; all the other 2378-substituted isomers and the seven BCR congeners of PCBs were detected in the six samples analyzed. The PCDD, PCDF, and PCB contamination of soils was lower than that assessed in sewage sludges, with total TEQ levels ranging between 0.3 and 8.6 pg/g. The dioxin and furan recoveries were similar to those obtained in sewage sludge samples, ranging between 86 and 106%. The concentrations of PCDDs, PCDFs, and PCBs in soils were determined before and after the application of sewage sludges, and a general increase was observed with the applied rate. The I-TEQ values of sludge-treated areas were 1.2-2.8 times higher than the respective values of the noncontaminated areas for the basic experiment and from 7.4 to 11.6 for the acid experiment. The latter values were consistent with the data obtained by Albrecht et al. (26), who found a factor increase of 10. If the results were expressed on an organic matter basis, the increases in final soil concentrations will not be so great. For the basic experiment, the factor increase would be lower than 1.6, and for the acid experiment it would be, lower than 3.9.

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TABLE 3. Concentrations of PCDDs, PCDFs, and PCBs (Expressed in Dry Weight) in Initial and Final Soil Samples BIS

a

BFS(L)

BFS(H)

AIS

AFS(L)

AFS(H)

2378-TCDD 12378-PeCDD 123478-HxCDD 123678-HxCDD 123789-HxCDD 1234678-HpCDD OCDD 2378-TCDF 12378-PeCDF 23478-PeCDF 123478-HxCDF 123678-HxCDF 234678-HxCDF 123789-HxCDF 1234678-HpCDF 1234789-HpCDF OCDF

NQa 0.3 0.3 1.3 1.0 3.5 E01 1.6 E02 4.5 0.6 1.5 3.6 1.4 2.7 0.1 8.7 0.7 1.6 E01

Results Expressed in pg/g (dw) NQ 0.2 NQ 0.8 0.3 1.0 2.5 6.0 2.0 3.7 7.6 E01 1.7 E02 8.8 E02 2.1 E03 4.4 7.1 0.9 1.1 0.9 2.2 2.5 4.3 0.9 2.0 1.4 2.8 0.4 0.1 1.7 E01 2.7 E01 0.9 1.4 4.0 E01 5.9 E01

NQ 0.1 0.1 0.2 0.2 2.7 1.3 E01 0.5 0.1 0.1 0.3 0.1 0.1 NQ 2.1 0.2 1.5 E01

NQ 0.4 0.2 1.9 1.6 4.6 E01 4.6 E02 2.3 1.2 0.4 1.3 0.5 0.9 0.1 7.4 0.4 2.0 E01

NQ NQ 0.3 3.2 2.5 7.7 E01 7.9 E02 5.1 2.4 0.5 2.5 0.8 1.3 0.4 1.2 E01 0.7 2.8 E01

PCB 28 PCB 52 PCB 101 PCB 118 PCB 153 PCB 138 PCB 180 total PCBs

0.1 0.1 0.1 0.2 0.2 0.3 0.2 6.7

Results Expressed in ng/g (dw) 0.1 0.1 0.2 0.4 0.3 0.8 1.3 1.8 1.0 1.9 1.7 3.1 1.4 2.0 2.9 E01 5.7 E01

0.1 NDb 0.1 0.1 0.1 0.1 0.1 5.6

0.1 0.1 0.6 1.2 1.3 1.8 1.3 6.0 E01

0.2 1.4 0.9 1.6 1.7 2.6 1.2 9.9 E01

total PCDDs total PCDFs R(I-TEQ PCDDs/I-TEQ PCDFs) total PCDDs + PCDFs

0.9 2.1 0.4 3.1

Results Expressed in pg of I-TEQ/g (dw) 2.1 5.5 1.7 3.1 1.3 1.8 3.8 8.6

0.1 0.2 0.6 0.3

1.5 0.9 1.7 2.4

2.2 1.6 1.4 3.7

NQ, not quantified (Rs/n < 3).

b

ND, not detected.

The measured TEQ values from the investigation of sludgetreated areas were compared with the limits proposed by the Federal Health Office (FHO) of Germany in the report published in 1991 (27). This report contains reference values and recommends action for agricultural and horticultural land uses and soil reclamation. For health reasons, the group considers it a long-term objective to reduce dioxin concentration to below 5 pg of TEQ/g (dw) of soil used for agricultural purposes. For this reason, 5 pg of TEQ/g (dw) was the established limit restricting the cultivation of certain vegetables, and 40 pg of TEQ/g (dw), the limit excluding the cultivation of all plants with the exception of those with very low transfer factors. The results of the soil investigation showed that, in the case of an initial soil with low contamination (0.3 pg of I-TEQ/g), the final soil did not exceed the limit and presented concentrations below the 5 of pg I-TEQ/g (2.4 and 3.7 pg of I-TEQ/g). But, in the case of an initial soil with considerable contamination (3.1 pg of I-TEQ/g), after an application with a high doses of sewage sludge, the final soil (8.6 pg of I-TEQ/g) exceeded the limit set at 5 pg of I-TEQ/ g, which restricts the cultivation of certain vegetables. It is interesting to notice the difference observed in the ratio R(I-TEQ PCDDs/I-TEQ PCDFs). Whereas the R < 1 showed higher levels of PCDFs in the initial soil samples, the inverse occurred when the sewage sludge is applied. The values of R ranging from 1.3 to 1.8 showed high PCDD contamination. This variation demonstrated the effect of the sewage sludge on the soil. Figure 1 shows the percent contribution of each homolog group in the total toxicity of the sample. Whereas there was a prevalence of furans in the initial soil, dioxins (especially, hexa-, hepta- and octa- isomers) prevailed in the final soils. This is the distribution observed in the applied sewage sludges. The fate of PCDDs and PCDFs in sewage sludges following agricultural application can be observed also with changes

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detected in the isomeric distributions. Figure 2 shows the HxCDD and HpCDF patterns for the initial soil, final soil, and one of the sewage sludges applied. The HxCDD pattern in the BIS sample presents a principal contribution of 123468HxCDD, and the ratio with the 123679/123689-HxCDD is 1.67; the sewage sludge applied (BSS86) had a distribution dominated by the 123679/123689-HxCDD, the intensity of the 123468-HxCDD isomer being 10 times lower. As expected, the BIS pattern is affected by the sewage sludge pattern acquiring their characteristics. For this reason, in the BFS(H) sample, the 123679/123689-HxCDD is now the predominant isomer with a previous isomeric rate of 0.60. As for the HpCDF isomeric distribution, changes could be observed between the 1234678-HpCDF and the 1234689-HpCDF. In the BIS sample, 1234678-HpCDF is the predominant isomer, whereas in the BFS(H) both isomers contribute in the same proportion. The sewage sludge applied (BSS86) presented a high contribution of 1234689-HpCDF, corroborating the different behavior in the soil samples. These differences in isomer profiles may be useful in determining the PCDD and PCDF sources in contaminated soils. Thus, the comparison of ion chromatogram of soil samples before and after application allowed us to assess the influence of PCDDs and PCDFs in the sludge on the original soils. Estimate of Sewage Sludge Contribution to the PCDD and PCDF Concentration in Soil. The concentration of PCDDs and PCDFs in soils after the application of sludge is described by the following equation (28):

Csoil(t+1) ) Csoil(t) +

Csludge × ARy D × Sz × CF

(1)

where Csoil(t) is the soil concentration at time t (ng of I-TEQ/kg dw) (see Table 3); Csludge is the sludge concentration (ng of

FIGURE 1. Percentage contribution of each homologue group (tetra- to octa-chlorinated dioxin and furan) in the total toxicity of soil samples (a) and sewage sludge samples (b) involved in the acid experiment. I-TEQ/kg dw) (see Table 2); ARy is the application rate (kg/ ha) (see Table 1); Sz is the soil depth (cm) ) 20 cm; D is the soil density (kg/cm3) (see Table 1); and CF is the conversion factor (cm2/ha) ) 1 × 108 cm2/ha. It should be pointed that in these calculations no estimate of the degradation of PCDDs and PCDFs in soil has been included. Nor has the possibility of transformation from less toxic to more toxic isomers by photodegradation been assessed. The above equation can be applied as a preliminary prediction of soil contamination given the similar values obtained by theoretical estimates

and experimental analyses. The theoretical values obtained by applying this equation are given in Table 4. These results are similar to the experimental values with a factor increase of 2.0-2.6, but always in the same order of magnitude. The present study was based on experiments applying high contaminated sewage sludges (up to 100 pg of I-TEQ/g), exceeding the limit application rate of 5 ton/ha over a period of more than 3 years. Despite the incompliance of the German rules, the final soil was suitable for agricultural purposes in the case of initial soil with low contamination levels.

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FIGURE 2. Isomeric distribution changes observed between initial and final basic soils for (a) HxCDD and (b) HpCDF patterns.

TABLE 4. Comparison between Theoretical and Experimental pg of I-TEQ/g Values in Soil Samples after Sewage Sludge Application BFS (L) BFS (H) AFS (L) AFS (H)

theoretical value

experimental value

ratio

1.0 E01 1.8 E01 4.7 9.7

3.8 8.6 2.4 3.9

2.6 2.1 2.0 2.5

Therefore, no serious consequences are expected when these rules are complied with uncontaminated soils.

Acknowledgments The authors are indebted to the Escola Superior d’Agricultura from Barcelona, especially to Dra. T. Balanya` and to Dr. J. San ˜ a for their collaboration in this study. The assistance of Ignasi Espadaler and Francesc Ventura is also gratefully acknowledged.

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Received for review December 20, 1996. Revised manuscript received April 4, 1997. Accepted May 23, 1997.X ES9610601 X

Abstract published in Advance ACS Abstracts, July 1, 1997.

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