Environ. Sci. Technol. 1990, 24, 745-749
On-Site Treatment of Pesticide Waste and Rinsate Using Ozone and Biologically Active Soil Cathleen J. Somlch,’ Mark 1.Muldoon, and Philip C. Kearney
Pesticide Degradation Laboratory, Agricultural Research Service, USDA, Beltsville Agricultural Research Center, Beltsville, Maryland 20705 Pesticide waste and rinsate (PWR) obtained from a small farm was treated on site with ozone (18 h) and then circulated through a biologically active soil column (48 h). Concentrations of atrazine [2-chloro-4-(ethylamino)-6(isopropy1amino)-s-triazine],cyanazine [2-chloro-4-[(1cyano-(1-methylethyl)amino]-6-(ethylamino)-s-triazine], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)N-(2-methoxy-l-methylethyl)acetamide] were decreased from 17,30, and 82 ppm, respectively, to less than 5 ppm. The concentration of the other major pesticide component, paraquat (l,l’-dimethyL4,4’-bipyridiniumdichloride), decreased from 40 to 22 ppm. Laboratory studies showed that the rate of ozonation of these mixed pesticides was not first order as was observed in pure solutions. Ozonolysis yielded products that were much more amenable to biological degradation than parent material. Bioassays of treated solutions indicated that herbicidal activity was eliminated. No evidence of mutagenic activity was indicated in Ames assays. Introduction
A serious concern facing the agricultural farm community is the appearance of pesticide residues in ground and surface waters. Surface runoff, leaching, and point sources have all been indicated as processes contributing to this pollution. Point-source contamination can arise from poorly lined holding ponds, improper disposal of pesticide waste and rinsate, and pesticide spills. To eliminate these problems, many pesticide applicators have constructed wash pads for equipment that drain to a holding facility, but very few methods have been developed to treat this large amount of dilute mixed rinsate. An economical and effective method is therefore urgently needed to dispose of pesticide waste. Evaporation or concentration is not an effective alternative because concentration affords a slurry of highly concentrated waste. In addition, some pesticides are evaporated and are merely displaced to the atmosphere. In either case the activity of the pesticides remains. To detoxify the waste, the chemical must be altered. Unfortunately, some pesticides are resistant to microbial mineralization. Ozonolysis of certain pesticides has been shown to afford products that are more amenable to biological degradation and thus significantly enhances their rates of mineralization in soil (I,2). A system is under development in which pesticide rinsates are treated with ozone and the products placed on a biologically active soil column for further degradation (3). Test solutions of 100 ppm Aatrex (atrazine) or 100 ppm Lasso (alachlor) were used to demonstrate the potential effectiveness of this system. The purpose of this study is to examine the rate of pesticide degradation, to assess the toxicity of the products, and to determine the overall effectiveness of this process as a disposal method for pesticide waste and rinsate obtained from a small farm. Methods and Materials Source of Pesticide Waste and Rinsate (PWR).
Formulated pesticide concentrates were obtained from the University of Maryland, Maryland Agricultural Experiment Station, CMREC, BARC-Facility, Beltsville, MD 20705 (Hayden Research Farm). Analytical standard pesticides (>98% pure) were obtained from the Pesticide Reference Standards Laboratory, EPA, OPP, Analytical Chemistry Section, BARC-East, Beltsville, MD 20705. A rinsate volume reduction (RVR) facility was constructed at the Hayden Research Farm, which consisted of three 6048-L carboy holding/settling tanks interconnected by PVC tubing and associated pumps. The housed facility serves as the collection station for all pesticide waste and tank rinsate from pesticide spray operations on site. Several gallons of the PWR were removed from the RVR to be used in preliminarylaboratory tests and to determine the approximate concentrations of the various pesticides present. Analysis of PWR. Concentrations of pesticides were measured by high-pressure liquid chromatograpy (HPLC) using a Waters 4-pm (8 mm X 10 cm) C-18 Novapak column, a Waters 660 pump controller, two Waters 6000 pumps, and a Waters 990 UV/vis detector with a NEC-I11 controller. A 3-min gradient (Waters curve 6) from 25 to 75% acetonitrile in ion-pair solvent at a flow rate of 2 mL/min was used for routine analysis. The ion-pair solvent consisted of an aqueous solution of 0.27 M orthophosphoric acid, 0.13 M diethylamine, and 0.013 M sodium heptanesulfonate. These formulated pesticides were monitored: Aatrex Nine-0 (atrazine, CIBA-GEIGY Corp., Greensboro, NC 27409), Banvel (dicamba, Velisicol Chemical Corp., Chicago, IL 60611), Bladex 90DF (cyanazine, Shell Chemical Co., Houston, TX 77001), Dual 8E (metolachlor, Ciba-Geigy Corp.), Gramoxone Super (paraquat, IC1 Americas, Inc., Wilmington, DE 19897),Lasso Microtech (alachlor, Monsanto Agricultural Products Co., St. Louis, MO 63167), Ortho Malathion 5E (malathion, Chevron Chemical Co., San Francisco, CA 94105), Pounce EC (permethrin, FMC Corp., Philadelphia PA 19103), Princep 4L (simazine, Ciba-Geigy Corp., Greensboro, NC 27409); Treflan EC (trifluralin, Elanco Products Co., Indianapolis, IN 46285), and Weedone LV-4 (2,4-D, Union Carbide Agricultural Products Co., Inc., Research Triangle Park, NC 27709). Roundup Herbicide (glyphosate, Monsanto Agricultural Products Co., St. Louis, MO 63167) was measured according to an adaptation of the method described by Miles et al. (4). A 100-mL aliquot of the sample was made alkaline by the addition of 1.0 mL of 10 N KOH. The alkaline sample was extracted twice with 50-mL portions of CH,Gl,. The aqueous layer was concentrated just to dryness in vacuo and reconstituted to 5.0 mL with 0.02 M K2HP04. A 0.1-mL aliquot of this solution was placed in a 20-mL screw-cap vial to which 0.9 mL of 0.025 M borate buffer, pH 6.0, was added. Derivatization was carried out by adding 0.9 mL of acetone followed by 0.1 mL of 0.01 M 9-fluorenylmethyl chloroformate (Aldrich Chemical Co., Milwaukee, WI 53233). The solution was allowed to stand for 20 min prior to HPLC analysis, which was carried out with a Waters 10-pm (8 mm X 10cm) Bondapak-NH, Radial-Pak column and 40% acetonitrile
Not subject to U.S. Copyright. Published 1990 by the American Chemical Society
Environ. Sci. Technol., Vol. 24, No. 5, 1990 745
in 0.02 M KH2P04(pH 6.0) as solvent on the system described above. Ozonation of PWR (Small Scale). Conditions under which ozonation experiments were carried out were based on results obtained in previous experiments (2). Hydrogen peroxide (7 mL of 30%, 0.137 M) was added to 500 mL of PWR and the solution made alkaline (pH 10) with sodium carbonate buffer (20 mM). Ozonolysis was carried out in a 1-L graduated cylinder equipped with a stainless steel airstone on a Teflon feed tube. Ozone was generated by a Model GTC-1B ozone generator (Griffin Technics Corp., 178 Route 46, Lodi, NJ 07644) and added for 3 h a t a rates of ca. 2 pmol/min as measured by iodometric titration (5). Samples were removed a t various time intervals and analyzed by HPLC as previously described. Soil Metabolism of Ozonated PWR (Small Scale). [U-ring-14C]Atrazine and [methyl-14C]paraquat were purchased from Sigma Chemical Co., St. Louis, MO 63178. [U-ring-14C]2,4-D was purchased from California Bionuclear Corp., Sun Valley, CA 91352. [U-ring-14C]cyanazine was a gift of Shell Chemical Co., Houston, TX 77001. [U-ring-14C]metolachlor,[U-ring-14C]ammelide,and unlabeled ammelide were obtained gratis from Ciba-Geigy Corp., Greensboro, NC 27419. Aliquots (60 or 150 mL) of PWR (0.137 M hydrogen peroxide, 20 mM sodium carbonate, pH 10) were combined with 0.65 pCi of either radiolabeled atrazine, cyanazine, 2,4-D, or paraquat or with 1.36 pCi of radiolabeled metolachlor. Aliquots of 20 or 25 mL were removed and the remaining solutions ozonated according to the previously described conditions until the parent compounds could not be detected (45-60 min). Following ozonolysis, the solutions (ozonated and nonozonated) were fortified to 10 mM phosphate and buffered a t pH 7.0 with the addition of HCl. Soil metabolism studies were conducted in biometer flasks (6) containing 50 g of a 1:l mixture of sand and an unsterile Sassafras silt loam obtained from Salisbury, MD. The Sassafras silt loam soil, which was slightly acidic (pH 4.2), consisted of 14% organic matter, had a sand, silt, and clay content of 56, 20, and 24% , respectively, a moisture content of 57% at 1/3 bar, and a cation-exchange capacity of 16.6 mequiv/ 100 g. The clay mineral composition was not determined. The sand/soil mixture was amended with 5 mL of either the labeled ozonated or nonozonated PWR. Degradation was measured by trapping metabolic 14C02 in 10 mL of 0.1 N NaOH, which was counted via liquid scintillation. In a separate experiment, 25 mL of ozonated PWR was added to a biometer flask and fortified to 10 mM phosphate buffer (pH 7.0), 10 mM succinate, and Cook's trace metals (7). Another flask received a 25-mL solution fortified to 10 mM phosphate buffer (pH 7.0), 10 mM succinate, Cook's trace metals, and 0.5 mM ammelide. Both flasks were charged with 0.1 pCi of [14C]ammelideand 7 X 1O'O cells of Pseudomonas sp. strain A (7) in a 0.25-mL inoculum from a 5-mL culture grown overnight from a single plate colony. Ammelide metabolism was monitored by trapping metabolic '*C02 as described above. Plant Bioassay of PWR-Untreated and Treated. Greenhouse pots (10.2 cm X 10.2 cm X 10.2 cm) containing five to six wheat plants (six replications) or two to four soybean plants (five replications) were used to 2-weeks postemergence. The following solutions were applied topically a t a rate of 35 mL/m2 (40 gal/acre): (1)distilled water (control), (2) PWR untreated, (3) PWR treated with ozone for 2 h and neutralized, and (4) PWR treated with ozone for 2 h, neutralized, and circulated through a soil column for 24 h at a rate of 30 mL/min. Ozonation and 748
Environ. Sci. Technol., Vol. 24, No. 5, 1990
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Figure 1. Diagram of the iarge-scale ozonation and soil metabolism unit. Key: (1) air compressor for ozone generator (four outlet air drying columns not shown), (2) ozone generator (water cooling system not shown), (3) gas dispersion pipe and sparger tube, (4) ozonation chamber, (5) pesticide waste and rinsate (PWR), (6) transfer pump, (7) soil column, (8) stainless steel cylinder for suspending the soil column over the catchment reservoir, (9) catchment reservoir, (10) transfer pump, (11) air compressor for aerating the catchment reservoir, (12) multiple power outlet strip, (13) wood platform, (14) AC 115-V outlet.
microbial degradation were carried out in the small-scale reactor. The above four solutions were also applied directly to soil a t a rate of 75 mL/m2 (80 gal/acre) and the soil mixed. Soybean and wheat seeds were planted and covered with treated soil. Ames Assay of PWR-Untreated and Treated. Ames assays were carried out by Karl A. Traul, Genetic Toxicology Group, American Cyanamid Co., Agricultural Research Division, Princeton, N J 08540. The following solutions were screened for microbial mutagenicity by the Ames method (8-10): (1) untreated PWR, (2) PWR treated with ozone and neutralized, (3) PWR treated with ozone, neutralized, and passed through the soil column, (4) untreated synthetic pesticide mixture (SPM), (5) SPM treated with ozone and neutralized, and (6) SPM treated with ozone, neutralized, and passed through the soil column. Ozone and soil treatments were identical with those used in the plant bioassay. SPM consisted of 100 ppm active ingredient of the following formulated pesticides: Aatrex Nine-0, Bladex 90DF, Dual 8E, Lasso Microtech, Gramoxone Super, and Weedone LV-4. Tests were conducted using five strains of Salmonella typhimurium and one strain of Escherichia coli with and without metabolic activation. Postive and negative controls were run concurrently. Ozonation and Soil Metabolism of PWR (Large Scale). The large-scale ozonation/soil metabolism unit used in the study was similar to that used previously ( 3 ) with some modification. The system consisted of an ozonation chamber, a soil column, and various accessories (Figure 1). The ozonation chamber was fashioned from a 55-ga (208-L) 316 stainless steel (SS) drum (James T. Waring and Sons, Capitol Heights, MD 27431). The ozone generator (PCI Ozone Generator Model GL-lB, PCI Ozone Corp., West Caldwell, N J 07006) was operated with dry air feed gas. The ozone dispersion pipe in the chamber was fitted with a 15.2-cm length, 1.9-cm diameter, 10-pm pore gas sparger tube (Mott Metallurgical Corp., Farmington, CT 06032). The soil column consisted of a 64-cm diameter, 61-cm-high galvanized steel cylinder with a perforated bottom and contained, layered from top to bottom, the following: 5 kg of gravel (ca.average diameter, 0.75 cm), 75 kg of 50% Sassafras slit loam/sand mixture, 5 kg of gravel. The soil column was suspended over the catchment reservoir by a stainless steel cylinder (316 SS 55-gal drum with both ends removed), which was situated on top of four clay bricks. The catchment reservoir
measured 61 cm in height and 109 cm in diameter. Two air compressors, 40.5 L/min at 110 psi maximum output (Pneumotive Model No. LGH-210-H02, Air Power Products, Monroe, LA 71203), and two transfer pumps, 95 L/min capacity (Model TBS-E, Thompson Chemtrex, Inc., Erie, PA 16501), were also used. The entire system was mounted on a wood platform with a 91 cm X 305 cm base and a 91 cm X 91 cm shelf. In each of the five degradation experiments, 114 L of PWR was pumped from the RVR system into the ozonation chamber. The solution was fortified to 13.1 mM hydrogen peroxide and made alkaline with sodium carbonate buffer (20 mM) pH 9.5-10. The ozone generator was operated at 11-15 psi, 14.2 L/min, and at 100% ozone output (ca. 19 g/h). Drying columns for the air feed on the ozone generator were changed as needed. Ozonolysis was carried out for 18 h; subsequently, the solution was fortified to 10 mM potassium phosphate and the pH adjusted to 6.5-7.5 with the addition of 12 M HC1. The solution was transferred by pump to the catchment reservoir of the soil column and circulated for 48 h. After soil column treatment, the solution was transferred to a dedicated tank in the RVR system for evaporation. Samples were taken for HPLC analysis throughout ozonolysis, and prior to and after soil column treatment. After the completion of five 114-L batch reactions, the soil was removed from the column and analyzed for parent materials. Three extraction schemes were followed. (1) To 14.25 g of mixed wet soil (moisture content 43.33%) was added 115 mL of 6 N HC1 and extraction by mechanical wrist shaker proceeded for 60 min. The extract was filtered through glass fiber filter paper (Whatman 934-AH, 9 cm) and the filtrate evaporated in vacuo just to dryness. The residue was reconstituted in 5 mL of 10 mM phosphate buffer (pH 7.0) and assayed by HPLC. (2) To 27.06 g wet soil was added 100 mL acetonitrile-water mixture (9:l) and extraction by mechanical wrist shaker proceeded for 60 min. The extract was filtered through glass fiber filter paper and the filtrate collected and evaporated in vacuo just to dryness. The residue was reconstituted in 5 mL of acetonitrile and analyzed by HPLC. (3) To 27.06 g wet soil was added 100 mL of distilled water and extraction by mechanical wrist shaker proceeded for 60 min. The aqueous extract was filtered through glass fiber filter paper and the filtrate collected and evaporated in vacuo just to dryness. The residue was reconstituted in 1 mL of acetonitrile and analyzed by HPLC. Results and Discussion
Laboratory Studies. According to farm records, rinsates from 12 pesticides (alachlor, atrazine, cyanazine, 2,4-D, dicamba, glyphosate, malathion, metolachlor, paraquat, permethrin, simazine, and trifluralin) were discarded in the RVR unit. Although analyses were carried out for all of these compounds, only four were detected: atrazine, cyanazine, metolachlor, and paraquat. 2,4-D was observed in initial analysis but by midsummer (2 months later) the concentration in the RVR was below the detection limit and was not included in this study. Microbial degradation is most likely responsible for the disappearance of 2,4-D. When the pesticide waste and rinsate (PWR) was treated with ozone, the rate of parent disappearance did not follow first-order kinetics (Figure 2). A pronounced lag time was observed for metolachlor and atrazine and less of one for cyanazine. The rate of paraquat ozonolysis is very slow and it is difficult to conclude that the rate increases with time as it does for the others. This rate
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Figure 2. Treatment of 500 mL of PWR with ozone at pH 10, 20 mM sodium carbonate and 0.137 M hydrogen peroxide. (0)atrazine; (0) cyanazine; (B) metolachlor; (A)paraquat.
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Flgure 3. Soil metabolism of [U-ring-14C]metolachlorin PWR. (0) no treatments; (0)ozonated.
acceleration is in contrast to previous studies where ozonolysis of all four herbicides was examined individually (2, 11-13). In these cases, the disappearance of parent material followed pseudo-first-order kinetics; that is, assuming the concentration of ozone and other oxidants (OH', HO;, OF, etc.) in solution remains constant, the rate of substrate disappearance in dilute concentrations becomes dependent upon the concentration of substrate alone, d[S]/dt = k' [SI, where k' = k,[03] + k2[OH'] + k3[H02'] + k4[0
