Illinois Fertilizer
Conference Proceedings
January 28-30, 1991
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Allan S. Felsot1
The utility of landfarming for detoxifying pesticide waste in soil was examined at an agrichemical facility in Piatt County, Ill. Soil contaminated with the herbicides alachlor, atrazine, metolachlor, and trifluralin was excavated, and various amounts were applied to an adjacent field divided into corn and soybean plots. Dissipation of residues, phytotoxicity to crops and weeds, bioaccumulation in grain, and quality of shallow groundwater were monitored after application of the contaminated soil.
Data from soil-treated subplots was compared to data from subplots in which herbicides were freshly sprayed. Herbicides did not dissipate significantly in excavated soil that had been stockpiled on the ground. Microbial assays of the contaminated soil showed low bacterial populations and inhibited soil dehydrogenase. After two years, alachlor and metolachlor concentrations in subplots with the highest application rate of contaminated soil were significantly greater than concentrations in the corresponding freshly-sprayed subplots. In subplots with the lowest application rate of contaminated soil, alachlor and metolachlor persistence did not differ significantly from persistence in freshly-sprayed plots with recommended application rates.
Some phytotoxicity to soybeans was noted from the heaviest loadings of waste soil, but freshly-applied herbicides caused significantly more damage. Yields were not adversely effected by application of contaminated soil. Greenhouse bioassays of diluted waste soil showed little phytotoxicity to corn or soybeans; however, bioactivity against weed species was high. Residues of parent herbicides did not bioaccumulate in grain, and herbicide levels in shallow groundwater were not affected by soil treatment.
Potential problems with landfarming of herbicide waste included prolonged persistence of herbicide residues in soil at high application rates and crop phytotoxicity when a diverse mixture of herbicides were present. A laboratory experiment indicated that addition of an organic nutrient amendment may enhance the biodegradation of herbicides after contaminated soil is landfarmed.
An estimated 1,500 agrichemical retail outlets are located throughout Illinois. These facilities provide farmers with a variety of services including the custom application of fertilizers and pesticides. Incidental spillage of product during mixing, loading, and rinsing operations is common and results in the accumulation of high concentrations of potentially hazardous chemicals in the soil. When present in the soil at-unusually high concentrations, biodegradable chemicals can be extremely persistent, which increases the risk of surface and groundwater contamination (Wolfe et al. 1973; Staiff et al. 1975; Davidson et al. 1980; Schoen and Winterlin 1987; Felsot and Dzantor 1990). Indeed, the Illinois Department of Public Health has found excessively high levels, of pesticides in agrichemical facility wells and nearby residential wells (Long 1989). Furthermore, the Illinois Environmental Protection Agency (IEPA) receives many complaints about runoff from agrichemical facilities resulting in fish kills or causing damage to vegetation on neighboring properties. Ideally, agrichemical retailers should construct facilities for containing spills during routine operations and for recycling of waste pesticides in rinse water.
The Illinois Department of Agriculture recently implemented containment regulations that will help allay pesticide contamination at commercial facilities; some facilities, however, are already contaminated and need cleanup. In addition, individual farms may face similar problems of pesticide contamination, especially near well heads. Excavation and landfilling, the usual methods of remediation, are expensive and do not address the problem of chemical detoxification. More permanent solutions would involve decontamination by landfarming (also known as land application or land treatment), chemical treatment, biological treatment, or combinations thereof.
Typical problems faced by agrichemical facilities were demonstrated at the Galesville Chemical Co. (GCC) in Piatt County, Ill. (Felsot et al. 1988). Soil to a depth of lm along a railroad-right-of-way at the GCC facility had been found by the IEPA to be contaminated with unacceptably high levels of herbicides (e.g., 24,000 ppm alachlor in the top 10 cm, 100 ppm at a depth of 60 cm). The herbicides were discharged to this area as a waste stream arising from the mixing, loading, and cleaning operations of GCC. Pesticide residues were detected in the ditches lining the streets of Galesville (population<500), and trace levels were detected in two water wells. IEPA ordered excavation and clean-up of the site.
To avoid obtaining a special waste permit and hauling contaminated soil to a municipal landfill, the Illinois Natural History Survey collaborated with IEPA and the management of GCC to landfarm the contaminated soil in corn and soybean plots on an adjacent farm. The soils were excavated and stored on the ground in piles, which were sampled to determine residue levels and microbial activity.
After application of contaminated soil to soybean and corn plots, herbicide residues were monitored in the soil, in shallow groundwater, and in the harvested grain. Phytotoxicity against crops and weeds was also determined. A follow-up laboratory study tested the feasibility of enhancing herbicide biodegradation by adding organic nutrient amendments to soil during landfarming, a technique commonly known as biostimulation.
Site description: GCC drained waste water from loading and tank rinsing operations onto a railroad right-of-way along the eastern edge of its property. Soil in this area, which covered approximately 1,215 m2. was excavated and stored on the ground at the site in four piles that were numbered 1-4. Each pile of soil was designated wastepile soil 1-4.
After excavation, the site was backfilled with soil from an adjacent fence row that was at a higher elevation and presumed not to be contaminated from the waste-water discharges. Waste-pile soil 2, which contained the highest levels of herbicides, was excavated from the top 60 cm of an area encompassing 122 m2 and was used in subsequent land application experiments. Contaminants included alachlor, atrazine, metolachlor, and trifluralin.
During the spring of 1986, a four-acre field adjacent to the railroad right-of-way and to the north of the waste piles was divided into two, 2-acre fields for land application of waste-pile soil 2. The field had been planted to corn in 1985 and chisel plowed in the fall. In 1986, the southern half of the field was designated for corn production and the northern half was designated for soybeans. The soil was a mixture of Ipava silt loam and a Sable silty clay loam with an organic carbon content of 3.1 percent and moisture content of 22.6 percent w/w at 0.3 bar. Waste-pile soil had an organic carbon content of 5.6 percent and a moisture content of 30.3 percent w/w at 0.3 bar.
The corn and soybean plots were further subdivided into three replicated blocks containing six subplots, (12.3m x 12.3m or 40 ft x 40 ft), that were treated with contaminated soil or freshly sprayed with herbicides (see below for details of the treatments). Each plot was surrounded by a 6.2m x 6.2m untreated buffer zone. Corn and soybeans were planted within one week of soil and spray applications. Each plot contained 16 crop rows spaced 76cm apart.
After the crop was harvested in 1986, the plots were left untilled, and benchmarks placed so that plots could be re-established in the same positions during the 1987 crop year. In May, the field was treated with paraquat to burn down perennial weeds. On June 10, 1987, the field was prepared by chisel plowing in a north-south direction, parallel to the old crop rows. The field was disked twice, first diagonally to the old rows and then parallel to the rows. Untreated border areas around each plot prevented soil from one subplot from contaminating an adjacent subplot. Corn and soybeans were planted along the north-south direction on the same day. No further applications of soil or herbicides were made. Shallow wells (less than 11 ft) were placed in corn plots only; well installation and depths have been previously described (Felsot et al. 1988).
Application of waste-contaminated soil: Persistence of herbicide residues in landfarmed, contaminated soil was compared to persistence of herbicides that were freshly sprayed with amounts calculated to yield concentrations in soil similar to those in waste-pile soil 2. Rates of application were determined on the basis of the alachlor concentration since it was the most prevalent contaminant. Treatments were designated by the following codes:
(1) CHECK: untreated soil;
(2) lx-N: herbicide spray mixture applied in 1986 at the rate normally recommended
for alachlor; 3.36 kg a.i./ha; the mixture consisted of alachlor, atrazine,
metolachlor, and trifluralin in proportion to the concentrations found in waste-pile
soil 2 in May, 1986 (74, 48, 17, and 3g herbicide/g oven-dry soil [ods], respectively,
Felsot et al. 1988);
(3) 5x-N: herbicide spray mixture applied in 1986 at 18.6 kg a.i./ha, i.e., five times the recommended alachlor rate;
(4) lx-S: contaminated soil from waste-pile 2 applied at the equivalent alachlor rate of 3.36 kg a.i./ha;
(5) 2.5x-S: waste-pile soil applied at the equivalent alachlor rate of 8.4 kg a.i./ha;
(6) 5x-S: waste-pile soil applied at the equivalent alachlor rate of 18.6 kg a.i./ha
Soil was applied with a manure spreader. The spreader was filled by using a front loader that was calibrated by weighing the entire loader with and without a full load of soil. Within 24 hours after application of contaminated soil and herbicide sprays, all plots were disked twice in two directions to incorporate the pesticides and soil. Buffer zones were also disked, which served to clean equipment and minimize cross-contamination between treatment plots.
Soil and water sampling, preparation, storage: Soils were collected from field plots with a 5-cm diam. bucket auger during 1987 and early 1988. Two subsamples of soil from depths of 0-15cm and 15-30cm were collected from each replicated subplot. The subsamples were combined in the field and returned to the laboratory on the same day. The auger was washed with methanol between subsamples taken by soil depth and between different subplots. Soils were sieved through a 3mm mesh screen and stored at 2°C for up to one month prior to extraction. Herbicide residues remained stable under these conditions for at least four months (Felsot et al. 1988).
Sampling of well water during the growing season and grain following harvest have been previously described in detail (Felsot et al. 1988). Water and grain samples were stored at -20°C prior to analysis.
Extraction, Analysis, and Quantitation of Herbicide Residues: Some 50g of soil were slurried with 20mL of distilled water and extracted twice with 90mL of ethyl acetate as described by Dzantor and Felsot (1989) for methyl carbamate insecticides. Water (300mL) was extracted twice with ethyl acetate (100mL). Ground corn and soybean were macerated with acetonitrile, partitioned with hexane, and cleaned on Florisil (Felsot et al. 1988).
All herbicides were qualitatively analyzed--by packed-column gas-liquid chromatography (GLC, Packard Model 328) with nitrogen-phosphorus specific detection. Residues were separated on a 90cm x 0.2mm i.d. glass column packed with 5 percent Apiezon + 0.1 percent DEGS maintained isothermally at 190°C. Residues were quantitated by the method of external standards, which were used to calibrate the GLC response each day of analysis..
Phytotoxicity measurements: Field observations of crop injury and weed control ratings in corn and soybean plots were made during June and August of 1986 using recommended procedures (Frans 1972). During July of 1987, observations were made only in soybean plots.
Measurement of microbial biomass and soil enzyme activities in waste pile soil and treated plots: Methods were described by Dzantor and Felsot (in press). Briefly, bacterial numbers in soil treatments were estimated by the plate dilution frequency assay (Harris and Sommers 1968), using soil extract agar (Lockhead 1940), and fungi were enumerated by the soil dilution, pour-plate method using rose-bengal streptomycin agar (Martin 1950). Dehydrogenase activities in the soils were measured by the amount of triphenylformazan (TF) formed after incubation of soil with triphenyltetrazolium chloride (Frankenberger and Johanson 1986). Esterase activity was measured as the amount of fluorescein formed when soils were incubated in the presence of fluorescein diacetate (Schnurer and Rosswall 1982). Urease activity was determined by a modified non-buffer method (Zantua and Bremner 1975) with measurement of the NH3 released when soil samples were incubated with urea.
Effect of corn and soybean plant residues on dissipation of alachlor in contaminated soil from GCC: A laboratory experiment was designed to test the effects of organic nutrient amendments on degradation of aged residues of alachlor and metolachlor in waste-contaminated soil under simulated landfarming conditions. Soil was collected from the untreated portions of the field where the landfarming experiment was conducted; this soil was identified as check soil. The source of environmentally-aged residues of alachlor and metolachlor was the soil stored in piles at the GCC facility near the field plots (i.e., waste-pile soil). This soil had been stored at 4°C in the laboratory approximately three years before use. Check soil and waste-pile soil were stored without drying and passed through a 3mm mesh screen before use.
Waste-pile soil (P) was diluted by mixing with check soil (C) in the following proportions: 1P:9C (90 percent dilution), 1P:1C (50 percent dilution), 9P:1C (10 percent dilution), 100P:OC (0 percent dilution). Then 30g oven dry-equivalents of moist diluted or undiluted soil were weighed into 250mL Erlenmeyer flasks. Soils were left unamended or amended with ground corn or soybean plant residue at an application rate of 2 percent w/w. Soil moisture was adjusted to 30 percent w/w. All treatments were prepared in triplicate. All flasks were covered with Parafilm and opened for aeration at weekly intervals. Soil moisture was adjusted to approximately 33 percent. After 32 days of incubation at 25°C, samples were extracted with ethyl acetate and analyzed by previously described procedures (Felsot and Dzantor 1990a).
During the planning of the landfarming experiment, we developed four criteria
for successful remediation of the herbicide-contaminated soils: (1)No significant
difference after one growing season between herbicide residues in soil from
waste-treated plots and freshly sprayed plots.
(2) No contamination of suggested by U.S. EPA;
(3) No significant residues in grain;
(4) No significant toxicity to crops as measured by phytotoxicity assays in
the field or greenhouse and by comparison to yields from the untreated check
plots.
Herbicide residues in soil: Soil samples collected within a day after application of waste-pile soil and herbicide sprays afforded a comparison of the initial concentration of herbicides found in all experimental plots compared to the theoretical amounts corresponding to the various rates of application. On the basis of a 3.36kg a.i./ha application rate (i.e., lx treatment), the soil to a depth of 15cm should have contained theoretically 1.71, 4.28, and 8.55 ppm of alachlor for a lx, 2.5x, and 5x application rate, respectively. The percentage of theoretical recovery ranged from 33.6 percent for the 5x-S soybean treatment to 113 percent for the lx-N corn treatment. Percentage of theoretical recovery for,all treatments combined was 66.5+/-23.0 percent.
Another concern was the initial concentration of herbicides in soil-treated plots compared to the corresponding treatments in sprayed plots. With the exception of the 5x-S and 5x-N alachlor treatments in the soybean plots, there were no significant differences in recovery of herbicides between soil-applied and sprayed herbicide on Day 0 in the top 15cm of the profiles (only data for alachlor and metolachlor are shown, Figure 1 and 2). Nearly twice as much alachlor was recovered from the 5x-N treatment in the soybean plot as from the 5x-S treatment. This difference may reflect sampling error because concentrations of alachlor recovered later from the 5x-S treatment were much higher than the initial recoveries (Figure l).
During the first 140 days of sampling, high variability precluded the detection of significant differences between corresponding rates of application of fresh herbicide and contaminated soil. By days 380 and 520, however, significantly more alachlor and metolachlor were recovered from 5x-S treatments than from 5x-N treatments (Fig. 1, 2). No statistically significant differences were seen between lx-N and 1x-S or 2.5x-S treatments, although the latter two were often numerically greater than the lx-N treatment (data not shown). Recovery of the other herbicides did not differ significantly among treatments on these sampling days. Residues at the 15-30cm depth did not differ among treatments.
The three-to-10 fold greater recoveries of alachlor and metolachlor from the 5x-S treatment than from the 5x-N treatment suggested that the residues in the aged, contaminated soil were less available to microbial degradation. The residues recovered 1.5 years after application were more than half of what would be expected after a recommended application rate of 3.36kg si/ha. The prolonged persistence of alachlor and metolachlor in waste-pile soil and in the field plots is not characteristic of the comparatively rapid degradation of these compounds when used at normal rates of application. Alachlor half-life generally ranges from 2-4 weeks (Sharp 1988), and it is less persistent than metolachlor, whose half-life is highly variable (13-108 days) depending on moisture and temperature conditions (LeBaron et al. 1988). on the other hand, several studies have shown that high concentrations of pesticides, which are characteristic of waste, are unusually persistent (Davidson et al. 1980, Stojanovic 1972, Junk et al 1984, Schoen and Winterlin 1987; Wolf et al. 1973). In our study, alachlor and metolachlor were still found in waste-pile 2 at concentrations of 23 and 17ppm, respectively, two years following excavation.
Two hypotheses were developed to explain the prolonged persistence of alachlor and metolachlor in the waste-pile soils and in the field plots. First, studies of high concentrations of pesticides in soil have shown that microbial populations can be severely reduced, which may be the critical factor for explaining the prolonged persistence of those chemicals (Stojanovich 1972; Davidson et al. 1980; Dzantor and Felsot [in press]).
We hypothesized that the microbial populations in the waste-pile soils were reduced as a 'result of exposure to toxic concentrations of the herbicides. On the other hand, the inhibition of microbial populations does not explain adequately the prolonged persistence of the herbicides after mixing waste-pile soil with uncontaminated soil by land application. The herbicides in waste-pile soil could be considered to be aged (Smith et al. 1988), i.e., the chemicals were in contact with the soil for an extended period of time. Aged residues have been shown to be less desirable (McCall and Agin 1985; Steinberg et al. 1988) and in some cases seem to degrade more slowly than freshly-applied chemicals (Steinberg et al. 1988, Byast and Hance 1981). Thus, a second hypotheses, but not mutually exclusive of the first, ascribes the slow degradation of the herbicides to a lack of pesticide bioavailability upon aging in the soil.
Herbicide residues in shallow groundwater: Atrazine and alachlor were found in some wells, including the check well, two days after the application of waste-pile soil and the spraying of herbicides (Felsot et al. 1988). Concentrations of both compounds exceeded the suggested U.S. EPA MCLs (2ppb for alachlor and 3ppb for atrazine). Since the wells were not purged before sampling at this time, these residues may have translocated over time owing to past farming practices. Indeed, all herbicides present in waste-pile soil were also detected in untreated check soil on day 2. After 41 days, concentrations were below suggested MCLs. No significant differences in atrazine or alachlor concentration in well water were found among soil treatments throughout 140 days of monitoring. Trifluralin and metolachlor were not detected in any well sample. Other research that employed tile drain sampling has shown that herbicide residues are frequently detected in shallow groundwater (Muir and Baker 1978); therefore, detection of atrazine and alachlor in all wells was not unusual.
Herbicide residues in grain: Residues in harvested corn and soybean were very low (limit of quantitation was Sppb; data not shown; Felsot et al. 1988). Residues were not detected in grain from the untreated checks, and atrazine was not detected in any treatment. Only alachlor was above the limit of quantitation in the 2.5x-S and lx-N treatment for corn and soybean, and residues in grain were not related to soil treatment.
Phytotoxicity: Weed control and crop phytotoxicity were used as indicators of potential bioactivity of herbicide residues in contaminated soil. A previous technical report that discussed the first nine months of the landfarming project concluded that herbicide residues in the contaminated soil (i.e., waste-pile soil) were biologically active (Felsot et al. 1988). For example, weeds were well-controlled in the field by application of waste-pile soil alone (Table 1), and significant toxicity was observed against several sensitive weed species (velvet leaf, foxtail, and pigweed) in greenhouse bioassays even after diluting the soil 97 -percent with untreated soil (Felsot et al. 1988).
During the second year of the study (i.e., the second growing season after application of waste-pile soil), control of pigweed and velvetleaf in the 5x-S soybean plots was still higher than in the 5x-N plots, which suggested the presence of comparatively greater levels of herbicide residues in waste-treated plots than in freshly-sprayed plots (Table 2).
Soybeans were noticeably injured in 2.5x-S and 5x-S treatments, but phytotoxicity in plots treated with waste-pile soil was generally lower than phytotoxicity in plots freshly sprayed with herbicide (lx-N and 5x-N treatment, Table 1). By the second growing season, no phytotoxicity was observed in soybean plots (Table 2). Insignificant injury to corn was observed during the first growing season and was not related to rate of herbicide application (Table 2). In greenhouse assays, corn and soybeans were injured by waste-pile soil even after dilution by 50x with untreated soil; however, in freshly-treated soil, soybean and corn injury were observed after dilution by 94 percent with untreated soil (data not shown; Felsot et al. 1988).
Corn and soybean yields were used as another indicator of phytotoxicity. No differences in corn yields among soil,treatments were detected, but the 5x-N treatment in soybeans caused nearly total loss of bean yield owing to the high levels of atrazine (Felsot et al. 1988). A corresponding yield loss was not seen in the 5x-S treatment. Yields were not determined after the second growing season.
Microbial bioactivity: Microbial population size and bioactivity were significantly reduced in waste-pile 2 and 4 compared to the untreated check soil from the soybean plot (Table 3). These determinations were made on soil collected approximately one year after the start of the landfarming experiment. Both bacterial and fungal numbers were more than an order of magnitude lower in waste-pile sail than in check soil. On the other hand, the microbial numbers in the 1x-S and 5x-S soils was greater than that of the waste-pile soil and the check. The difference from the check may be explained by the fertilizer contamination in the waste pile soil, which probably stimulated microbial biomass once the waste-pile soil was diluted in the soybean plot with uncontaminated soil. Urease activities in all the soil treatments were nearly identical, but the activities of soil dehydrogenase and esterase were more than an order of magnitude lower in the waste pile soils than in check soils. Dehydrogenase activity, like biomass, was elevated in soil from the lx-S and 5x-S subplots.
The low estimates of microbial numbers in waste-pile soil and low> levels: of dehydrogenase activity suggested that the high concentrations of herbicides, although considered biodegradable, were maintained for many years in the contaminated soil at GCC because of low microbial numbers and act activity some degradation may have occurred after each input of herbicide-contaminated rinsewater, but the rates of biodegradation in the soil adjacent to the GCC facility may have been very slow. In recent experiments alachlor concentrations of 1,000 and 10,000ppm significantly inhibited soil dehydrogenase activity (Felsot and Dzantor 1990, Dzantor and Felsot [in press]). The similarity between rate of alachlor degradation when applied to soil either as technical-grade material or as an emulsifiable concentrate suggested that microbial toxicity resulted directly from exposure to alachlor itself rather than from the formulation additives (Felsot and Dzantor 1990a).
The seemingly prolonged persistence of alachlor and metolachlor in waste treated plots and the apparent low microbial bioactivity in waste-pile soil suggested further studies were needed to investigate augmenting the rate of dissipation during the landfarming process and perhaps even in contaminated soil itself. In previously published research, corn and soybean plant residue significantly enhanced the dissipation rate of 100 ppm rate of fresh residues of alachlor (Felsot and Dzantor 1990a). In contrast, when herbicides residues were environmentally aged, such as those present in waste-pile soil, dissipation could not be enhanced by organic amendments (Felsot and Dzantor 1990b). When, laboratory-aged soil contaminated with 10,000 ppm alachlor for less than one year was diluted first and then amended with corn plant residue, alachlor dissipation significantly increased compared to dissipation in unamended soil (Felsot et al. 1990).
In this study, dissipation of alachlor and metolachlor was significantly faster in waste-pile soil diluted by 90 percent with check soil and amended with corn plant residue than in soil diluted by 0, 10, or 50 percent and either amended with soybean residue or left unamended (Figure 3). These observations suggested that landfarming, which is essentially dilution of contaminated soil by mixing with uncontaminated soil, may be aided by adding extra nutrient sources to the soil.
Landfarming holds promise for disposing of pesticide-contaminated soils. Most of the criteria set for success were met: residues of herbicides in shallow ground water were not affected by landfarming; excessive residues were not found in grain; crop phytotoxicity was, tolerable and did not affect yield.
Persistence of alachlor and metolachlor residues in plots treated with waste-pile soil at five times the normal rate for alachlor, however, seemed prolonged compared to freshly-sprayed herbicides. Herbicide residues did dissipate from initially observed levels, but a third growing season would have been needed to determine if concentrations declined to levels not significantly different from the check. Lower application rates of waste-pile soil gave residues after one year that were not significantly different than residues from freshly sprayed herbicides.
Enhancement of alachlor and metolachlor dissipation in the presence of ground corn plant residues suggested that a combination of biostimulation and landfarming may further augment the degradation rate of waste pesticides in soil, especially when aging of pesticide residues may slow the rate of biodegradation. More studies are needed with different mixtures of herbicides to determine the safest and most efficient methods for landfarming of fresh and aged pesticide waste.
Technical contributions were provided by Dr. E. Kudjo Dzantor, Ms. Laurie Case, and Chris Chorney of the Illinois Natural History Survey and Drs. Rex Liebl and Tom Bicki of the UI Dept. of Agronomy. This research was supported in part by the Illinois Hazardous Waste Research and Information Center, projects no. HWR 86-023 and HWR 88-042.
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