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Boletín de la Sociedad Chilena de Química

versión impresa ISSN 0366-1644

Bol. Soc. Chil. Quím. v.45 n.4 Concepción dic. 2000

http://dx.doi.org/10.4067/S0366-16442000000400005 

CHEMICAL CHARACTERIZATION OF A MUNICIPAL LANDFILL
AND ITS INFLUENCE ON THE SURROUNDING ESTUARINE
SYSTEM, SOUTH CENTRAL CHILE.

Hernán Palma-Fleming1, Eduardo Quiroz1, Elena Gutierrez1, Erik Cristi1, Bernardo Jara1, María L. Keim2, Mario Pino2, Anton Huber2, Eduardo Jaramillo3, Osvaldo Espinoza1, Pedro Quijón3, Heraldo Contreras3 and Carlos Ramirez4.

Universidad Austral de Chile, Facultad de Ciencias, 1Instituto de Química, 2Instituto de
Geociencias, 3Instituto de Zoología, 4Instituto de Botánica, Casilla 567, Valdivia, Chile.
(Received: June 28, 2000 - Accepted: July 24, 2000)

SUMMARY

The spatial and temporal variations of cyclic organochlorine compounds, heavy metals, total hydrocarbons, surfactants, oil and grease, BOD5 (biochemical oxygen demand), dissolved oxygen and nutrients were measured during summer and winter of 1996 from the Valdivia municipal landfill and its surrounding estuarine system. During summer it was found that solid and liquid samples usually contained higher average contents for most of chemical parameters than winter samples, with the exception of oil and grease and Pb from leachate samples. Generally, samples from the landfill showed higher levels of chemical parameters than samples from the Futa River. High levels of heptachlor (52.1 ng/g and 31.5 ng/g during summer and winter, respectively) and endosulfan sulphate (127.4 n/g and 11,5 ng/g during summer and winter, respectively) were observed in sediments from a maximum depository zone of a small river adjacent to the landfill which receives the percolated leachates. The temporal variability (summer-winter) showed a significant dilution of pollutants, probably due to rainfall during winter. Estuarine benthos species, Mulinia edulis (clams) and cancer coronatus (crabs) showed low levels for most metals, except Zn in both species, Ni in clams, Cu and As in crabs. Significant levels of total BHC, 4,4’-DDE, aldrin, endrin ketone and heptachlor epoxide were observed in Mytilus chilensis (mussels).

Key words: Pollution, Valdivia River Estuary, municipal landfill, chemical characterization, organochlorine pesticides, heavy metals.

RESUMEN

Se determinó la variación espacio-temporal de compuestos organoclorados cíclicos, metales pesados, hidrocarburos totales, surfactantes, aceites y grasas, demanda bioquímica de oxígeno (DBO5), oxígeno disuelto y nutrientes en el vertedero municipal de Valdivia y su sistema estuarial colindante durante las estaciones de verano e invierno de 1996. Durante el verano se encontró que los parámetros químicos de las muestras sólidas y líquidas fueron mayores que las de invierno, con la excepción de aceites-grasas y Pb en muestras de percolados. En general, las muestras de las celdas del vertedero también mostraron niveles mayores de los parámetros medidos que los correspondientes al Río Futa. Se encontraron niveles altos de heptacloro (52,1 ng/g en verano y 31,5 ng/g en invierno) y endosulfan sulfato (127,4 ng/g en verano y 11,5 ng/g en invierno) en sedimentos provenientes de una zona de máxima deposición de un riachuelo cercano que recibe directamente los percolados del vertedero. La variación temporal (verano-invierno) indicó una significativa dilución de los contaminantes, probablemente debido a aguas lluvia durante el invierno. La especies bentónicas del estuario Mulinia edulis (almeja) y Cancer coronatus (jaiva) presentaron niveles de concentración de metales pesados relativamente bajos, excepto Zn en ambas especies, Ni en almejas, Cu y As en jaivas, mientras que se encontraron niveles significativos de BHC totales, 4,4’-DDE, aldrín, endrín cetona y heptacloro epóxido en Mytilus chilensis (choritos).

INTRODUCTION

The chemical characterization of solid wastes and leachates from municipal landfill operations poses concern when considering the environmental impact of these activities on aquatic ecosystem. When water percolates through such wastes, it dissolves organic and inorganic components thereby producing contaminated lactates whose successful treatment, to decrease its potential for contamination, will depend mostly on its chemical composition. Several studies have investigated the potential degree for pollution on ground water, surface water and toxic effects on aquatic organisms 1-6. Many factors are claimed to affect this properties like the composition, age, height, amount, moisture content, hydrogeology and climate of the site, sampling methods, rainfall and ground water dilution, and decontamination during passage through soil 7-10.

Landfills are biochemical closed systems, while aging, aerobic and anaerobic process occur in successive stages, producing gas and many decomposing products that can be even more toxic than its parental compounds. Chemical parameters like biochemical oxygen demand (BOD5), dissolved oxygen, nutrients (nitrogen and phosphorus), oil and grease and hydrocarbons as well as some minor toxic constituents (heavy metals and organochlorine compounds) will give useful information on the state of biochemical transformations occurring within the landfill and indicate the contaminants that should be removed from leachates. Seasonal variations should also be considered as such variations in leachate composition can be superimposed onto the long-term changes resulting from the various phases of biochemical decomposition producing a potential overloading of a treatment plant. A proper design of a leachate treatment plant will require information about the level and temporal variability of chemical composition of both landfill solid wastes and leachates.

The Valdivia River Estuary (ca. 40º S) is the largest one on the Pacific coast of South America; it is a very dynamic and partially mixed estuary with several interconnected rivers, which result in a hydrographic basin of 13,135 Km2 11. Since the estuary is actually a source of drinking water as well as it sustains a variable and complex fauna, many of them of commercial value, it will be useful to study potential sources of pollution. It is well known that contaminants might be in the neighborhood of the water supplier or might be many kilometers away. Some chemical contaminants have been reported in relatively few studies of sediments and benthos organisms of the estuarine system, showing low to medium levels of organochlorine compounds, for which the constituents most frequently found were S BHC (a-BHC + b-BHC + g-BHC + d-BHC), S DDT (4,4´-DDE + 4,4´-DDT + 4,4´-DDD), aldrin and DCB 12, 13, as well as heavy metals (Fe, Cu, Zn, Cr) 14. Organochlorine pesticides are of concern for humans because some of them show increased risk of cancer and/or antiestrogenic activity 15, 16. Valdivia city, including the coastal area (ca. 130,000 total habitants) deposit all commercial, industrial, hospital and residential residues in the Valdivia Municipal Landfill about 23 Km South East from downtown. Percolated leachates are finally discharged into the Futa River, one of the adjacent interconnected rivers of the estuarine system, and therefore it could present an environmental hazard.

The study of the landfill as a source of contaminants is necessary to protect human health and the environment. The main objectives of the present study were: (1) to characterize the chemical composition and physical parameters of solids and raw leachates from old and recent landfill area; (2) to investigate the seasonal variability of chemical composition of solids and leachates; (3) to investigate the potential for contamination of the surrounding estuary; and (4) to generate valuable data for leachate treatment.

EXPERIMENTAL

Area of study

The Valdivia municipal landfill is located in Morrompulli, about 23 Km South East from downtown (ca. 39°S) (Fig. 1a). The landfill began to operate in 1980 and it has a total surface of ca. 14,226 m2 divided into a recent and old area of about 8,763 m2 and 5,463 m2 respectively. The landfill is allocated at the top of a hill and it is made of big terraces of compacted waste at more than 15 m above the road, having an estimated volume of solid waste of 113,920 m3 and 81,845 m3, respectively. Previous non-published data on statygraphical analysis, temperature, field capacity, humidity content and apparent density of the landfill show a very heterogeneous refuse. The total solid waste of urban origin (commercial, industrial, hospital and domestic waste) is a composite of variable amount of organic matter (50 %), plastic (7 %), metal (3.4 %), glass (3.6 %), paper (8.3 %) and cloth pieces, wood and solid unknown particles (23.9 %) as the most important fraction 17. The old landfill area was sealed off in 1996. It is an unlined landfill and leachates percolate down to the base through multiple natural underground drainage streams. The percolated water merge in a single drainage built during 1994, which deliver leachate into a natural stream that flows toward the Futa river estuary (about 2000 m down the landfill area) (Fig. 1b).


Sampling stations

Triplicate samples were taken at each sampling station. Glassware and materials used for sampling and transport were cleaned following standard instructions given by each analytical method used in this study.

The sampling site consisted of nine test cells during summer and six test cells during winter of 1996; each cell of 5 m to 6 m deep with base dimensions 3 m x 1.5 m, excavated by means of a mechanical dragger. Test cells 1 and 2 were allocated in the old area while test cells 5, 6, 7 and 8 were allocated in the dumping recent area (Fig. 2). Control samples were collected from cells at points about 10-30 m outside the landfill (cells 3, 4, 9 and 10). During the summer of 1996, samples were collected from cells 1 to 9. During winter of the same year samples were collected from cells 1, 2,3, 7, 9 and 10. During winter no leachates could be taken from cells 1, 7 and control cells, since water level was not sufficient for hand sampling neither for vacuum pump sampling.

Burden percolated leachate samples were taken at sampling station B, at the single flow drainage allocated at the base of the landfill (Fig.1b). A control station (A) was located at 20 m upstream from station B. Sampling station C was at 2 km downstream from station B and about 100 m before reaching Futa River (Fig. 2).


Seven sampling stations were chosen at selected points of the estuarine system around Valdivia: stations D and E were in the Futa River estuary (Fig. 1b), F and G in the Calle-Calle River estuary, and H, I, and J in the Valdivia River estuary (Fig. 1a). Water samples were taken at each station by using a hydraulic bomb on surface water (about 30-50 cm deep), while sediments were taken by semi-autonomous diving. Stainless steel and high polymer cores were used to collect surface sediments (ca. 10 cm depth) for organochlorine and heavy metals analyses, respectively. Three organisms, the bivalves Mytilus chilensis and Tagelus dombeii and the crab Cancer coronatus were collected from station J (Fig. 1a) for pollutant analyses on soft tissues. Samples were preserved until analysis according to standard procedures described in each analytical method.

Chemical Analysis

Landfill solid waste and sediments were analyzed for oil and grease (soxhlet extraction-gravimetric), total hydrocarbons (soxhlet-infrared) and surfactants (soxhlet extraction-MBAS, adapted) according to standard methods 18, organochlorine pesticides (ECD-gas chromatography) 13 and heavy metals (atomic absorption spectrometry) 14. Test cell leachates, drained leachate (bulk) and estuarine waters were analyzed for BOD5, total nitrogen (macro-Kjeldhal), total phosphorous (vanadomolybdophosphoric acid colorimetric), oil and grease (partition-gravimetric), total hydrocarbons (partition-infrared), surfactants (anionic surfactants as MBAS), organochlorine pesticides and heavy metals (atomic absorption spectrometry) by standard methods 18. Organochlorine pesticides were not analyzed in estuarine waters. The soft tissues of benthos organisms, Mytilus chilensis, Tagelus dombeii and Cancer coronatus were analyzed for organochlorine compounds (ECD-gas chromatography) 12, just samples of Cancer coronatus were analyzed for heavy metals 19. Certified reference materials were used to validate analytical methods. The recoveries of organochlorine pesticides in certified marine sediment NIST SRM-1941a were more than 70 % with a variation coefficient of less than 8 % and for certified fauna tissue NIST SRM-2974 (Mytilus edulis) the recoveries were more than 65 % with a variation coefficient of less than 10 %. The relative percentage of error of heavy metals in certified dogfish standard reference material for trace metals, DOLT-1 from the National Research Council Canada, Division of Chemistry, Marine Analytical Standards Program was about 5 %. The standard addition method was used when certified materials were not available for protocol validation. Estimated detection limits (EDL) for organochlorine pesticides were typically 0.2 ng/g dry weight and 5 ng/L based on DDT for solid and liquid samples respectively and 0.02 ng/g based on DDT for wet weight of soft tissue. Limits of detection (LD) for heavy metals were typically between 0.01 mg/g and 0.25 mg/g for solid samples and between 0.05 mg/L and 10 mg/L for liquid samples.

RESULTS AND DISCUSSION

Solid waste were characterized by a high content of oil and grease, low levels of hydrocarbons and detergents, high levels of endosulfan sulphate, a-BHC, b-BHC, 4,4’-DDE, dieldrin, endrin aldehyde, endosulfan sulphate and heptachlor, and high levels of Fe, Zn, Cu, Cr, Ni and Pb (Table 1). Lower concentration of trace organochlorines and heavy metals were observed during winter when compared to the summer season, probably due to a dilution effect produced by rainfall. During winter, the average percolated flux was 2.2 L/s, and under a 50 mm/day rainfall the leaving flux was 20.8 L/s, while a 109 mm/day rainfall produced 86.1 L/s of leaving flux. Therefore, the observed dilution rate produced by rainfall during winter was between 9.5 and 39.1 times compared to the average percolated flux. However, oil and grease, hydrocarbons and detergents presented higher levels than the summer situation, indicating that these components were dependent on degradation process. Temperature measured on leachate from test cells indicated that oxidative reactions were occurring readily in summer than winter (Table 2). During summer, the average percolated leachate temperature in the recent area was about one and half higher than the temperature measured during winter (25.5 ºC and 18 ºC in sampling point 7, respectively) and about twice the temperature measured in the control point (14.9 ºC). DBO5, Kjeldahl-N and phosphorous indicated a significant high organic charge during summer and winter situations (Table 2). No surfactants were detected in leachates during summer and winter, suggesting that these components were readily degraded.



Relatively high concentrations of cyclic organochlorine compounds were found in solid waste coming from the old and recent area of the landfill. The highest concentration levels were found during summer; endosulfan sulphate (297.2 ng/g in cell 2), 4,4’-DDE (47.9 ng/g in cell 8) and b-BHC (36.4 ng/g in cell 5) were present in significant amounts (Table 1). Leachate analyses corroborated the presence of these and other compounds like d-BHC, aldrin and endosulfan I (Table 3). The control area did not show organochlorine compounds. The percolated flux from the single drainage (bulk leachate) in station B only showed endosulfan sulphate in relatively high concentration, and the remaining organochlorines were at concentrations below the estimated detection limit (5 ng/L). Station A (control station) did not show any presence of organochlorine pesticides.


Sediments data from station C (Table 4) showed that leachates were delivering organochlorine compounds into the estuary. Sediments are known to trap semi volatile chemicals, especially when high organic matter deposition occurs, as is the case in point C (Fig. 2) 13. High concentration of endosulfan sulphate was found in this station (127.4 ng/g), together with heptachlor, a-BHC, d-BHC, 4,4’-DDD, endrin, endrin aldehyde and endosulfan II. Endosulfan sulphate is normally produced by bacterial and fungal degradation of endosufan 20, and it has been reported that sediment adsorption is the principal route of endosulfan sulphate from water 21. Nevertheless its low solubility in water, it should be considered that some fishes are very sensitive to this compound (LC5 = 1 mg/L). Therefore a high concentration level of endosulfan sulphate, in addition to any other organochlorine pesticides found in sediments, represent a high risk of adverse effects over low trophic level organisms of the estuarine system close to the landfill. Low levels of organochlorine compounds were found in sediments (Table 5) and benthos filtering organisms (Table 4) of Corral Bay, with the exception of S BHC (total hexachlorocyclohexane isomers), 4,4’-DDE, aldrin, endrin ketone and heptachlor epoxide in Mytilus chilensis and g-BHC and d-BHC in sediments, whose concentration levels in station H, I and J (Fig. 1a) are coincident with previous studies on the contamination of the Valdivia Estuarine System. They have been suggested to come from louse treatment in humans, cattle and other agricultural activities 12, 13, and probably they do not come directly from the landfill-percolated effluent. Organochlorine pesticides are of special concern because they represent a group of semi-volatile persistent organic pollutants (POP) that moves long distances and condense over colder regions of the earth. The high concentration of organochlorine pesticides makes the landfill a potential reservoir that, when released, put concern for the toxic effects to humans and the environment.



Data for most of the heavy metals in the old and new refuse area were significantly superior to those of the control area. Fe was the most significant metal being found, followed by Zn, Cu, Cr, Pb and Ni, and minor quantities of As, Hg, Cd and Se (Table 1). The presence of these metals has been reported in variable concentrations in other municipal landfills 22. The last four elements in addition to Pb and Cr (VI) are considered priority pollutants 23. Even thought, these contaminants are subjected to dilution when reaching the estuarine system, some of them can be accumulated in sediments and biota organisms. Percolated waters in station B (Fig. 1b) show low levels input of heavy metals (Table 4), but considering the average leaving flux of 2.2 L/s during winter, these may represent an important contribution of contaminants to the ecosystem. Furthermore, the concentration level of these metals in sediments of station B and C does not show trapping effects, especially the last station, which seems to be a maximum deposition zone for organochlorine pesticides. Heavy metals were evenly distributed between stations A, B and C and their concentration levels compare well with a similar landfill in the City of Moncton, Canada that influence the bank of the Petitcodiac River 22. In addition, concentration levels were evenly distributed in all stations of the estuarine system, with the exception of Cr, which was significantly high in station D and E but not in C and therefore could not be necessarily assigned to landfill influence (Table 5). The concentrations of these elements in estuarine waters were of no significance with the exception of Fe. Estuarine benthos species, Mulinia edulis (clam) and Cancer coronatus (crab), showed low levels for most metals, except Zn in both species, Ni in clams, Cu and As in crabs (Table 4). The levels of Hg, Pb and Cd corresponded closely with previous reports on other Chilean species 24.

The heterogeneity of the landfill, in relation to cells that characterize the different transformation stages of biological degradation and that represent different ages, refuse composition and water content, can be better accounted by the disparity of pH and DBO. In the recent refuse area, cell 6 had a pH 8.1 and a low level of DBO, suggesting that no accumulation of short chain fatty acids was occurring, while cell 7 showed an acidic pH and a DBO about six times higher than cell 6, indicating that probably partially ionized free fatty acids must be occurring at this point (Table 2). Furthermore, the concentration level of Fe in leachate from cell 6 is about ten times lower than the observed value at cell 7, suggesting that the former was in a higher biological degradation stage than cell 7. This is in conformity with observations in other landfills 1, 7. Percolated water in station B had a basic pH, while stations A and C showed acidic and neutral pH, respectively. These values are harmless to freshwater aquatic life, although the toxicity of other chemicals in the ecosystem may be affected by changes between pH 6.5 and pH 9.0 25. In addition, the concentration levels of dissolved oxygen from stations A and C (Table 7) are between the normal values established for aquatic life protection, except station B, which were below the limit to avoid acute mortality to salmonids (Limit [O]DO = 6 mg/L) and at the limit of moderate production impairment (Limit [O]DO = 5 mg/L) to other life stages 25.

Relatively low concentration levels of total hydrocarbons in the landfill solid waste were found. This was comparable with those reported in other studies on the chemical characterization of landfills 1, 9 , except for cell 1 from the old area (273 mg/L) (Table 1). In this area, domestic waste like solvents, lubricants, cosmetics, lacquers, varnishes, insect repellents and mainly oil spills from transporting vehicles were found. Leachate showed high levels of total hydrocarbons in cell 6 (229 mg/L), however percolated water in station B (bulk leachate) showed low levels of these components; the highest value was found in station C during summer (59.6 mg/L). These results would suggest that most hydrocarbons in the landfill were being retained and/or decomposed and little accumulation was occurring in station C. Although oil spills can be periodically observed upstream of Futa River, it cannot be attributed to landfill emissions. During summer, estuarine water of stations E and I showed high concentration levels of hydrocarbons (1,443 mg/L and 955 mg/L, respectively). These high values in the estuarine system may be due to gasoline, diesel and oil spills from outboard boats and tourism small ships activities rather than contamination from the landfill. Qualitative headspace solid-phase micro extraction analysis for speciation purposes 26 showed the presence of BTEX components (benzene, toluene, ethyl benzene and isomeric xylenes) in most solid and liquid samples. No data on water quality criteria for protection of aquatic life are available for total hydrocarbons because there do not represent definitive chemical categories, but it is known that the highest proportion of aromatic components in any oil or solvent residue the highest is the toxicity. Many aquatic species can naturally accumulate contaminants that are in low concentration in the surrounding water and sediments, and hydrocarbons are no exception, especially when dispersed. Data from literature show that the most sensitive category of organisms are marine larvae, which appear to be intolerant to petroleum pollutants at concentrations as low as 0.1 mg/L and can harm aquatic life at concentrations as low as 1 mg/L 25. Fats and oils of animal or vegetable origin generally are non-toxic to aquatic life; however, high concentration of such oils may produce floating sheens that may result in deleterious effects 26. Percolated leachates (bulk leachate) showed low concentration of fats and oils of animal and vegetable origin (Table 4) in spite of the high concentration levels of these components in solid wastes and leachates (Tables 1 and 2), which strongly suggest efficient biochemical degradation inside the landfill as it has been observed in another landfill 7. Therefore, oil and grease from the landfill, at the time of this study would not represent a potential risk for aquatic organism of the estuarine system under study.

Kjeldahl nitrogen and total phosphorous showed higher concentration levels in leachates during summer compared to winter probably due to dilution effects (Table 2), but diminished values were observed for percolated waters (bulk leachate) (141.89 and 298.53 mg/L in summer and winter respectively) (Table 4). Most of the Kjeldahl nitrogen usually was in the ammoniacal form and probably came from the deamination of aminoacids during the acetogenic phase, reflecting active and continuous refuse degradation process inside the landfill 7. Both old and recent landfill area showed high values (the highest value was 2786 mg/L in cell 6). Dilution effects were significant when comparing cell 7 during summer and winter seasons (1915 mg/L and 329 mg/L respectively). These concentration levels are comparable from the reported values in other landfills by Chu et al. (885 mg/L) 7 and Hartmann and Hoffmann (1500 mg/L) 27. Concentrations of phosphorous were low in percolated waters. Since the optimal ratio of BOD5 to P for effective aerobic treatment is 100 to 1 27, 28, 29, addition of phosphate to percolated water during summer would be necessary to maintain the ratio at less than 100 to 1.

CONCLUSIONS

The concentration levels and temporal variations of cyclic organochlorine compounds, heavy metals, hydrocarbons, surfactants, oil and grease, as well as BOD5 (biochemical oxygen demand), dissolved oxygen and nutrients from the Morrompulli Municipal Landfill and the Valdivia Estuarine System measured in solid samples, percolated leachate (bulk leachate), cell leachate, and representative fauna over a one year period showed that a treatment plant would be needed to effectively remove organochlorine pesticides residues and heavy metals from percolated waters. Although most of the parameters under study decrease by rainfall dilution effects, the high volume of leaving percolated flux bring trace levels of persistent compounds to the estuarine system that represent high risk for aquatic life and potential adverse human health effects. Organic pollutants should be studied more deeply to better characterize those compounds that have high risk of environmental toxic effects, like BTEX, policyclic aromatic compounds (PAHs) and phenols. For effective aerobic treatment, the addition of phosphate to percolated water during summer would also be necessary.

ACKNOWLEDGMENTS

Most of this study was supported by MIDEPLAN (Ministerio de Planificación, Chile). The authors want to thank to Dirección de Investigación y Desarrollo, Universidad Austral de Chile (Projects S-94-35, S-95-34 and S-98-31) and the European Economic Comunity (Project CI1*CT93-0099) for the financial support for laboratory analyses.

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