Survival,reproduction, and recruitment of woody plants after 14 years on a reforested landfill

With the advent of modern sanitary landfill closure techniques, the opportunity exists for transforming municipal landfills into urban woodlands. While costs of fullscale reforestation are generally prohibitive, a modest planting of clusters of trees and shrubs could initiate or accelerate population expansions and natural plant succession from open field to diverse forest. However, among woody species that have been screened for use on landfills, these ecological potentials have not yet been investigated. We examined a 14-yr-old landfill plantation in New Jersey, USA, established to test tolerance of 19 species of trees and shrubs to landfill environments. We measured survivorship, reproduction, and recruitment within and around the experimental installation. Half of the original 190 plants were present, although survival and growth rates varied widely among species. An additional 752 trees and shrubs had colonized the plantation and its perimeter, as well as 2955 stems of vines. However, the great majority (>95%) of woody plants that had colonized were not progeny of the planted cohort, but instead belonged to 18 invading species, mostly native, bird-dispersed, and associated with intermediate stages of secondary plant succession. Based on this evidence, we recommend that several ecological criteria be applied to choices of woody species for the restoration of municipal landfills and similar degraded sites, in order to maximize rapid and economical establishment of diverse, productive woodlands.     

Management of old landfills by utilizing forest and energy industry waste flows

The lack of landfill capacity, forthcoming EU waste disposal and landfill management legislation and the use of non-renewable and energy intensive natural resources for the end-treatment of old landfills increase pressures to develop new landfill management methods. This paper considers a method for the end-management of old landfills in Finland, which is based on the utilization of forest and paper industry waste flows, wastes from paper recycling (de-inking) and wastes from forest industry energy production. Fibre clay wastes from paper mills, de-inking sludges from de-inking of recovered waste paper and incineration ash from forest industry power plants serve to substitute the use of natural clay for the building of landfill structures for closed landfills. Arguably, this method is preferable to existing practices of natural clay use for landfill building, because it (1) substitutes non-renewable natural clay, (2) consumes less energy and generates less CO2 emissions than the use of natural clay, and (3) eliminates considerable amounts of wastes from paper production, paper consumption and from forest industry energy production. Some difficulties in the application of the method are considered and the waste flow utilization is incorporated into a local forest industry recycling network.     

Effects of landfill gas on subtropical woody plants

An account is given of the influence of landfill gas on tree growth in the field at Gin Drinkers' Bay (GDB) landfill, Hong Kong, and in the laboratory. Ten species (Acacia confusa, Albizzia lebbek, Aporusa chinensis, Bombax malabaricum, Castanopsis fissa, Liquidambar formosana, Litsea glutinosa, Machilus breviflora, Pinus elliottii, andTristania conferta), belonging to eight families, were transplanted to two sites, one with a high concentration of landfill gas in the cover soil (high-gas site, HGS) and the other with a relatively low concentration of gas (low-gas site, LGS). Apart from the gaseous composition, the general soil properties were similar. A strong negative correlation between tree growth and landfill gas concentration was observed. A laboratory study using the simulated landfill gas to fumigate seedlings of the above species showed that the adventitious root growth ofAporusa chinensis, Bombax malabaricum, Machilus breviflora, andTristania confera was stimulated by the gas, with shallow root systems being induced.Acacia confusa, Albizzia lebbek, andLitsea glutinosa were gas-tolerant, while root growth ofCastanopsis fissa, Liquidambar formosana, andPinus elliottii was inhibited. In most cases, shoot growth was not affected, exceptions beingBombax malabaricum, Liquidambar formosana, andTristania conferta, where stunted growth and/or reduced foliation was observed. A very high CO₂ concentration in cover soil limits the depth of the root system. Trees with a shallow root system become very susceptible to water stress. The effects of low O₂ concentration in soil are less important than the effects of high CO₂ concentration.Acacia confusa, Albizzia lebbek, andTristania conferta are suited for growth on subtropical completed landfills mainly due to their gas tolerance and/or drought tolerance.     

Methane oxidation in two Swedish landfill covers measured with carbon-13 to carbon-12 isotope ratios

The release of methane (CH4) from landfills to the atmosphere and the oxidation of CH4 in the cover soils were quantified with static chambers and a 13C-isotope technique on two landfills in Sweden. One of the landfills had been closed and covered 17 years before this investigation while the other was recently covered. On both landfills, the tops of the landfills were compared with the sloping parts in the summer and winter. Emitted CH4, captured in chambers, was significantly enriched in 13C during summer compared with winter (P < 0.0001), and was enriched relative to anaerobic-zone methane. The difference between emitted and anaerobic zone delta 13C-CH4 was used to estimate soil methane oxidation. In summer, these differences ranged from 9 to 26@1000, and CH4 oxidation was estimated to be between 41 and 50% of the produced CH4 in the new landfill, and between 60 and 94% in the old landfill. In winter, when soil temperature was below 0 degree C, no difference in delta 13C was observed between emitted and anaerobic-zone CH4, suggesting that there was no soil oxidation. The temperature effect shown in this experiment suggests that there may be both seasonal and latitudinal differences in the importance of landfill CH4 oxidation. Finally the isotopic fractionation factor (alpha) varied from 1.023 to 1.038 and was temperature dependent, increasing at colder temperatures. Methanotrophic bacteria appeared to have high growth efficiencies and the majority of the methane consumed in incubations did not result in immediate CO2 production.     

Potential for enhanced phytoremediation of landfills using biosolids – a review

Despite the use of recyclable materials increasing worldwide, waste disposal to landfill remains the most common method of waste management because it is simple and relatively inexpensive. Although landfill disposal is an effective waste management system, if not managed correctly, a number of potential detrimental environmental impacts have been identified including soil and ground water contamination, leachate generation, and gas emissions. In particular, improper post-closure treatment of landfills or deterioration of the conventional clay landfill capping were shown to result in land degradation which required remediation to secure contaminants within the landfill site.Phytoremediation is an attractive technology for landfill remediation, as it can stabilize soil and simultaneously remediate landfill leachate. In addition, landfill phytoremediation systems can potentially be combined with landfill covers (Phytocapping) for hydrological control of infiltrated rainfall. However, for the successful application of any phytoremediation system, the effective establishment of appropriate, desired vegetation is critical. This is because the typically harsh and sterile nature of landfill capping soil limits the sustainable establishment of vegetation. Therefore, the physicochemical properties of landfill capping soils often need to be improved by incorporating soil amendments. Biosolids are a common soil amendment and will often meet these demanding conditions because they contain a variety of plant nutrients such as nitrogen, phosphate, potassium, as well as a large proportion of organic matter. Such amendment will also ameliorate the physical properties of the capping soils by increasing porosity, moisture content, and soil aggregation. Contaminants which potentially originate from biosolids will also be remediated by activities congruent with the establishment of plants and bacteria.     

Solid waste management in urban areas: Development and application of a decision support system

A decision support system (DSS) developed to assist the planner in decisions concerning the overall management of solid waste at a municipal scale is described. The DSS allows to plan the optimal number of landfills and treatment plants, and to determine the optimal quantities and the characteristics of the refuse that has to be sent to treatment plants, to landfills and to recycling. The application of the DSS is based on the solution of a constrained non-linear optimization problem. Various classes of constraints have been introduced in the problem formulation, taking into account the regulations about the minimum requirements for recycling, incineration process requirements, sanitary landfill conservation, and mass balance. The cost function to be minimized includes recycling, transportation and maintenance costs. The DSS has been tested on the municipality of Genova, Italy, and the results obtained are presented.     

Evaluation of alternative landfill cover soils for attenuating hydrogen sulfide from construction and demolition (C&D) debris landfills

Hydrogen sulfide (H(2)S) generated from C&D debris landfills has emerged as a major environmental concern due to odor problems and possible health impacts to landfill employees and surrounding residents. Research was performed to evaluate the performance of various cover materials as control measures for H(2)S emissions from C&D debris landfills. Twelve laboratory-scale simulated landfill columns containing gypsum drywall were operated under anaerobic conditions to promote H(2)S production. Five different cover materials were placed on top of the waste inside duplicate columns: (1) sandy soil, (2) sandy soil amended with lime, (3) clayey soil, (4) fine concrete (particle size less than 2.5 cm), and (5) coarse concrete (particle size greater than 2.5 cm). No cover was placed on two of the columns, which were used as controls. H(2)S concentrations measured from the middle of the waste layer ranged from 50,000 to 150,000 ppm. The different cover materials demonstrated varying H(2)S removal efficiencies. The sandy soil amended with lime and the fine concrete were the most effective for the control of H(2)S emissions. Both materials exhibited reduction efficiencies greater than 99%. The clayey and sandy soils exhibited lower reduction efficiencies, with average removal efficiencies of 65% and 30%, respectively. The coarse concrete was found to be the least efficient material as a result of its large particle size.     

Root growth and metal uptake in four grasses grown on zinc-contaminated soils

Depth and area of rooting are important to long-term survival of plants on metal-contaminated, steep-slope soils. We evaluated shoot and root growth and metal uptake of four cool-season grasses grown on a high-Zn soil in a greenhouse. A mixture of biosolids, fly ash, and burnt lime was placed either directly over a Zn-contaminated soil or over a clean, fine-grained topsoil and then the Zn-contaminated soil; the control was the clean topsoil. The grasses were 'Reliant' hard fescue (Festuca brevipila R. Tracey), 'Oahe' intermediate wheatgrass [Elytrigia intermedia (Host) Nevski subsp. intermedia], 'Ruebens' Canada bluegrass (Poa compressa L.), and 'K-31' tall fescue (Festuca arundinacea Schreb.). Root growth in the clean soil and biosolids corresponded to the characteristic rooting ability of each species, while rooting into the Zn-contaminated soil was related to the species' tolerance to Zn. While wheatgrass and tall fescue had the strongest root growth in the surface layers (0-5 cm) of clean soil or biosolids, wheatgrass roots were at least two times more dense than those of the other grasses in the second layer (5-27 cm) of Zn-contaminated soil. When grown over Zn-contaminated soil in the second layer, hard fescue (with 422 mg/kg Zn) was the only species not to have phytotoxic levels of Zn in shoots; tall fescue had the highest Zn uptake (1553 mg/kg). Thus, the best long-term survivors in high-Zn soils should be wheatgrass, due to its ability to root deeply into Zn-contaminated soils, and hard fescue, with its ability to effectively exclude toxic Zn uptake.     

Can urban tree roots improve infiltration through compacted subsoils for stormwater management?

Global land use patterns and increasing pressures on water resources demand creative urban stormwater management. Strategies encouraging infiltration can enhance groundwater recharge and water quality. Urban subsoils are often relatively impermeable, and the construction of many stormwater detention best management practices (D-BMPs) exacerbates this condition. Root paths can act as conduits for water, but this function has not been demonstrated for stormwater BMPs where standing water and dense subsoils create a unique environment. We examined whether tree roots can penetrate compacted subsoils and increase infiltration rates in the context of a novel infiltration BMP (I-BMP). Black oak (Quercus velutina Lam.) and red maple (Acer rubrum L.) trees, and an unplanted control, were installed in cylindrical planting sleeves surrounded by clay loam soil at two compaction levels (bulk density = 1.3 or 1.6 g cm(-3)) in irrigated containers. Roots of both species penetrated the more compacted soil, increasing infiltration rates by an average of 153%. Similarly, green ash (Fraxinus pennsylvanica Marsh.) trees were grown in CUSoil (Amereq Corp., New York) separated from compacted clay loam subsoil (1.6 g cm(-3)) by a geotextile. A drain hole at mid depth in the CUSoil layer mimicked the overflow drain in a stormwater I-BMP thus allowing water to pool above the subsoil. Roots penetrated the geotextile and subsoil and increased average infiltration rate 27-fold compared to unplanted controls. Although high water tables may limit tree rooting depth, some species may be effective tools for increasing water infiltration and enhancing groundwater recharge in this and other I-BMPs (e.g., raingardens and bioswales).     

GROUND AND SURFACE WATER QUALITY IMPACTS OF NORTH CAROLINA SANITARY LANDFILLS1

ABSTRACT: Ground and surface water quality monitoring data from 71 municipal sanitary landfills in North Carolina were analyzed to determine the nature and extent of current contamination problems and identify any common characteristics associated with this contamination. A total of 322 surface and 411 ground water quality records were analyzed using the SAS data system. Almost all the landfill records included inorganic and heavy metal analyses while approximately half of the records also included organic analyses by CC/MS. Our analysis indicates that landfills are having measurable impacts on ground and surface water quality, but these impacts may not be as severe as is commonly assumed. Statistically significant increases were detected in the average concentrations in ground water and downstream surface water samples when compared to upstream surface water samples. The largest percentage increases were observed for zinc, turbidity, total organic carbon, conductivity, total dissolved solids, and lead. Violations of ground water quality standards for heavy metals and hazardous organic compounds were detected at 53 percent of the landfills where adequate data existed. The moat common heavy metal violations were for lead (18 percent), chromium (18 percent), zinc (6 percent), cadmium (6 percent), and arsenic (6 percent) (percentage of landfills violating shown in parenthesis). The organic compounds that appear to pose the greatest threat to ground water are the chlorinated solvents (8 percent), petroleum derived hydrocarbons (8 percent), and pesticides (5 percent). A comparison of monitoring data from sanitary landfills and secondary wastewater treatment plants suggests that the concentrations of heavy metal and organic pollutants discharged to surface waters from these two sources are similar.     

Influence of Landfill Gas on the Microdistribution of Grass Establishment Through Natural Colonization

Many revegetated landfills have poor cover including bare areas where plants do not grow. This study, on the Bisasar Road Landfill site in South Africa, assessed grass species preferences to microhabitat conditions in a mosaic of patches of well-established grassed areas and bare, nonvegetated areas. Factors, including soil CO₂, CH₄, O₂, nutrients, and other general soil conditions, were measured in relation to species distribution and grass biomass in the field. Cynodon dactylon was the dominant grass in the established grass areas but was less abundant in the areas bordering the bare areas where Paspalum paspalodes and Sporobolus africanus were common. A number of soil factors measured were significantly correlated with grass biomass and these included Mg, Ca, Zn, Mn, K, temperature, moisture, and CO₂. However, a laboratory bioassay using the growth of C. dactylon with soils removed from the landfill indicated that there were no differences in the soils from the bare areas and those that supported high plant biomass. Thus, no nutrient deficiency or chemical toxicity was inherent in the soil in the laboratory. The results of the field investigation and bioassay indicated that soil CO₂ as a result of landfill gas infiltration into the root zone was probably the main factor causing bare areas on the landfill where no grass species could colonize and grow and that C. dactylon was more sensitive to elevated soil CO₂ than other grass species such as P. paspalodes and S. africanus.     

Soil water repellency induced by long-term irrigation with treated sewage effluent

This study describes soil water repellency developed under prolonged irrigation with treated sewage effluent in a semiarid environment. Soil surface layer (0-5 cm) and soil profile (0-50 cm) transects were sampled at a high resolution at the close of the irrigation season and rainy winter season. Samples from 0- to 5-cm transects were subdivided into 1-cm slices to obtain fine scale resolution of repellency and organic matter distribution. Extreme to severe soil water repellency in the 0- to 5-cm soil surface layer persisted throughout the 2-yr study period in the effluent-irrigated Shamouti orange [Citrus sinensis (L.) Osbeck cv. Shamouti] orchard plot. Nearby Shamouti orange plots irrigated with tap water were either nonrepellent or only somewhat repellent. Repellency was very variable spatially and with depth, appearing in vertically oriented "repellency tongues." Temporal and spatial variability in repellency in the uppermost 5-cm soil surface layer was not related to seasonality, soil moisture content, or soil organic matter content. Nonuniform distribution of soil moisture and fingered flow were observed in the soil profile after both seasons, demonstrating that the repellent layer had a persistent effect on water flow in the soil profile. A lack of correlation between bulk density and volumetric water content in the soil profile demonstrates that the observed nonuniform spatial distribution of moisture results from preferential flow and not heterogeneity in soil properties. Soil water repellency can adversely affect agricultural production, cause contamination of underlying ground water resources, and result in excessive runoff and soil erosion.     

Phytoremediation of aged petroleum sludge: effect of irrigation techniques and scheduling

The use of higher plants to accelerate the remediation of petroleum contaminants in soil is limited by, among other factors, rooting depth and the delivery of nutrients to the microsites at which remediation occurs. The objective of this study was to test methods of enhancing root growth and remediation in the subsurface of a contaminated petroleum sludge. The phytoremediation of highly contaminated petroleum sludge (total petroleum hydrocarbons >35 g kg(-1) was tested in the greenhouse as a function of the frequency and the depth of irrigation and fertilization. Water and dissolved plant nutrients were added to the soil surface or at a depth of 30 cm, either daily or weekly. Equivalent quantities of water and nutrients were added in all cases. Daily irrigation at a depth of 30 cm invoked greater root growth and enhanced contaminant degradation relative to all other treatments. In the absence of plants, residual concentrations of petroleum hydrocarbons after 7 mo were higher than with plants. The presence of plant roots clearly improved the physical structure of the soil and increased microbial populations. Thus, the plant roots in conjunction with daily additions of soluble N and P appeared to enhance oxygen transport to greater depths in the soil, stimulate petroleum-degrading microorganisms, and provide microbial access to soil micropores. Subsurface irrigation with frequent, small amounts of water and nutrients could significantly accelerate phytoremediation of field soils contaminated with petroleum hydrocarbons.     

Effects of tree root-derived substrates and inorganic nutrients on pyrene mineralization in rhizosphere and bulk soil

This study investigated the effects of organic and inorganic nutrients on the microbial degradation of the common soil contaminant pyrene. The material used in this investigation was collected from potted trees that had been growing for over a year in a soil artificially contaminated with polycyclic aromatic hydrocarbons. Soil was removed from the nonroot (bulk) and root (rhizosphere) zones of these pots and used in mineralization studies that tracked microbial degradation of 14C-pyrene. The factors influencing degradation in these zones were then tested by amendment with essential inorganic nutrients or with root-derived materials. As expected, pyrene mineralization was greater in soil removed from the rhizosphere than in bulk soil. The rate of mineralization in rhizosphere soil was inhibited by inorganic nutrient amendment, whereas nutrients stimulated mineralization in the bulk soil. Pyrene mineralization in bulk soil was also increased by the addition of root extracts intended to mimic exudation by living roots. However, amendment with excised fine roots that were allowed to decay over time in soil initially inhibited mineralization. With time, the rate of mineralization increased, eventually exceeding that of unamended bulk soil. Combined, the initial inhibition and subsequent stimulation produced a zero net impact of decaying fine roots on bulk soil mineralization. Our results, in conjunction with known temporal patterns of fine root dynamics in natural systems, support the idea that seasonal variations in nutrient and substrate availability may influence the long-term effect of plants on organic degradation in soil, possibly reducing or negating the beneficial effects of vegetation that are often observed in short-term studies.     

Soil and plant characteristics of landfill sites near Merseyside,England

An ecological survey of the plant and soil characteristics was carried out on three landfill sites near Merseyside, England. It was discovered that bare ground at two of the landfill areas had high levels of methane contained in the soil air (Sefton Meadows landfill: 6–8% at 35 cm and 16–35% at 65 cm below soil surface; Coalgate Lane landfill: 1–24% at 35 cm and 39–45% at 40 cm below soils surface), causing the appearance of dark grey reduced regions in the soil, a phenomenon similar to flooded soil. The wellvegetated areas at the two sites had lower levels of methane (under 7%).In areas relatively free of methane, the concentrations of mineralized N and NO₃ ^– had significant correlations with the dry weights of vegetation (r = 0.71 withp<0.01;r=0.61 withp<0.02 accordingly), indicating the necessity of applying available nitrogen fertilizer.     

Phytocapping: An alternative technique to reduce leachate and methane generation from municipal landfills

Avoiding percolation of water into refuse is the key function of landfill covers. ‘Phytocapping’ has been considered as an effective, economical and environment-friendly technique for landfill remediation. In this technique, trees are established on a layer of soil cap placed over the refuse. Soil cover acts as a ‘storage’ and trees act as ‘bio-pump and filters’. For effective functioning of this technique, it is critical that an ‘optimum’ depth of soil is placed over the refuse, and ‘suitable’ plant species are used as plant cover. Preliminary results of a phytocapping trial (using 21 tree species and two depths of soil layers) show that the established trees can remove more water than that received via rainfall and rainfall interception can reduce up to 20% of the rain reaching the soil in a 1.5 year old plantation. The study is also trialling an US numeric model ‘STOMP’ (Subsurface Transport over Multiple Phases), to calculate daily water balance, to identify suitable plant species and to optimise thickness of the soil cover to be used in phytocapping.     

MODELING OF LEAKAGE THROUGH CRACKED CLAY LINERS -I: STATE OF THE ART1

ABSTRACT: The existence and importance of macro-pores to the containment efficiency of cover clay liners at waste landfills is documented. Macro-pores exist as voids, or cracks, and act to increase the volume and rate of leakage through cover liners. Existing numerical models used to simulate flow through clay liners are shown to neglect the macro-pore aspect of the problem. Current theories of macro-pore flow developed from related areas of research are presented, and applications to the landfill liner problem are considered.     

Estimating Root Zone Soil Moisture at Continental Scale Using Neural Networks

This study investigates the feasibility of artificial neural networks (ANNs) to retrieve root zone soil moisture (RZSM) at the depths of 20 cm (SM20) and 50 cm (SM50) at a continental scale, using surface information. To train the ANNs to capture interactions between land surface and various climatic patterns, data of 557 stations over the continental United States were collected. A sensitivity analysis revealed that the ANNs were able to identify input variables that directly affect the water and energy balance in root zone. The data important for RZSM retrieval in a large area included soil texture, surface soil moisture, and the cumulative values of air temperature, surface soil temperature, rainfall, and snowfall. The results showed that the ANNs had high skill in retrieving SM20 with a correlation coefficient above 0.7 in most cases, but were less effective at estimating SM50. The comparison of the ANNs showed that using soil texture data improved the model performance, especially for the estimation of SM50. It was demonstrated that the ANNs had high flexibility for applications in different climatic regions. The method was used to generate RZSM in North America using Soil Moisture and Ocean Salinity (SMOS) soil moisture data, and achieved a spatial soil moisture pattern comparable to that of Global Land Data Assimilation System Noah model with comparable performance to the SMOS surface soil moisture retrievals. The models can be efficient alternatives to assimilate remote sensing soil moisture data for shallow RZSM retrieval.     

Fate of atrazine in sandy soil cropped with sorghum

A field study was conducted to determine the fate of atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) within the root zone (0 to 90 cm) of a sandy soil cropped with sorghum [Sorghum bicolor (L.) Moench] in Gainesville, Florida. Atrazine was uniformly applied at a rate of 1.12 kg ai. ha(-1) to a sorghum crop under moderate irrigation, optimum irrigation, and no irrigation (rainfed), 2 d after crop emergence. Bromide as a tracer for water movement was applied to the soil as NaBr at a rate of 45 kg Br ha(-1), 3 d before atrazine application. Soil water content, atrazine, and Br concentrations were determined as a function of time using soil samples taken from the root zone. Atrazine sorption coefficients and degradation rates were determined by depth for the entire root zone in the laboratory. Atrazine was strongly adsorbed within the upper 30 cm of soil and most of the atrazine recovered from the soil during the growing season was in that depth. The estimated half-life for atrazine was 32 d in topsoil to 83 d in subsoil. Atrazine concentration within the root zone decreased from 0.44 kg ai. ha(-1) 2 days after application (DAA) to 0.1 kg a.i. ha(-1) 26 DAA. Negligible amounts of atrazine (approximately 5 microg kg(-1)) were detected below the 60-cm soil depth by 64 DAA. Most of the decrease in atrazine concentration in the root zone over time was attributed to degradation. In contrast, all applied bromide had leached past the 60-cm soil depth during the same time interval.     

Degradation and mobility of linear alkylbenzene sulfonate and nonylphenol in sludge-amended soil

Degradation and mobility of the surfactants linear alkylbenzene sulfonate (LAS) and nonylphenol (NP) were investigated in a lysimeter study using a sandy loam soil and 45-cm soil columns. Anaerobically digested sewage sludge was incorporated in the top-15-cm soil layer to an initial content of 38 mg LAS and 0.56 mg NP kg(-1) dry wt., respectively. Spring barley (Hordeum vulgare L.) was sown onto the columns. The lysimeters were placed outdoors and therefore received natural precipitation, but were also irrigated to a total amount of water equivalent to 700 mm of precipitation. Leachate and soil samples from three soil layers were collected continuously during a growth period of 110 d. Leachate samples and soil extracts were concentrated by solid-phase extraction (SPE) and analyzed using high performance liquid chromatography (HPLC) with fluorescence detection. The concentrations in the top-15-cm soil layer declined to 25 and 45% of the initial contents for LAS and NP, respectively, within the first 10 d of the study. At the end of the study, less than 1% LAS was left, while the NP content was below the detection limit. Assuming first-order degradation kinetics, half-lives of 20 and 37 d were estimated for LAS and NP, respectively. The surfactants were not measured in leachate samples in concentrations above the analytical detection limits of 4.0 and 0.5 microg L(-1) for LAS and NP, respectively. In addition, neither LAS nor NP were measured in concentrations above the detection limits of 150 and 50 microg kg(-1) dry wt., respectively, in soil layers below the 15 cm of sludge incorporation, indicating negligible downward transport of the surfactants in the lysimeters.