Duane F. Berry

Nitrate removal in riparian wetland soils : effects of flow rate, temperature, nitrate concentration and soil depth

Abstract Riparian zones, located adjacent to intensely managed agricultural fields, are thought to play an important role in removal of nutrient contaminants including NO−3 from groundwater. We studied the effect of flow rate, NO−3 concentration and temperature on NO−3 removal in soil columns under saturated-flow conditions. Bibb (coarse-loamy, siliceous, acid thermic Typic Fluvaquent) sandy loam soil was collected from a riparian forest located in Nomini Creek Watershed, Virginia. Soils included in the study were a permanently inundated surface horizon, a seasonally saturated surface horizon, a shallow subsurface horizon and a deep subsurface horizon. Soil columns were infiltrated with NO−3 amended groundwater at concentrations from 14 to 36 mg NO−3-N L−1. Column operating temperatures varied between 8 and 20°C and flow rates between 0.01 and 0.09 mL min−1. Following a 48 h equilibrium period, effluent NO−3 and N2O concentrations were determined. Denitrification was the primary mechanism of NO−3 removal, with higher denitrification capacities found in the surface horizons. Effluent NO−3 concentrations could be described by a linear combination of temperature, flow rate and influent NO−3 concentrations. Low temperatures and increased flow rates reduced the denitrification capacity in all soils. Our results showed that the NO−3 removal capacity present in the Bibb soil should theoretically be sufficient to remove most, if not all, NO−3 from the groundwater at the Nomini Creek study site. However, on-site measurements of NO−3 concentration in receiving streams indicated that this capacity is not fully realized in the field, suggesting the importance of other factors such as local hydrology and groundwater flow patterns.

Denitrification potential of nontidal riparian wetland soils in the Virginia Coastal Plain

In the Atlantic Coastal Plain, riparian wetlands are thought to play an important role in the removal of NO−3 from groundwater. The denitrification potential of the Bibb (coarse-loamy, siliceous, acid, thermic Typic Fluvaquents) series, located in the Nomini Creek Watershed, Virginia, was evaluated in the laboratory using soil columns under saturated flow conditions. Soil columns were infiltrated with synthetic groundwater containing 3.2 ± 0.1 mmol NO−3-N (44 ± 2.0 mg NO−3-N l−1). Soil samples were collected from two surface horizons and one subsurface horizon in May (soil temperature 16.4°C), September (19.9°C), and November (13.5°C) of 1993 at 12 sites along the stream. Denitrification rates (N2O-N evolution in the presence of acetylene) were significantly higher for soils incubated at 19.9°C than at 16.4 or 13.5°C. The highest mean denitrification rates were measured in the ponded surface horizon (0.40 ± 0.17 μmol N2O-N (g DW)−1 d−1 at 16.4°C, 0.65 ± 0.27 at 19.9°C, 0.40 ± 0.25 at 13.5°C) in comparison to the terrestrial surface (0.17 ± 0.11, 0.28 ± 0.13, 0.16 ± 0.11) and subsurface (0.04 ± 0.02, 0.11 ± 0.06, 0.04 ± 0.01) horizons. Rates of denitrification were significantly correlated with organic carbon for the ponded surface horizon across all three temperatures. For the terrestrial surface and subsurface horizons, organic carbon was related to denitrification rates for only those soils incubated at 13.5°C. Relations between NO−3 loss and denitrification rates were present for the terrestrial surface horizon across all temperatures, and at 13.5 and 16.4°C for the ponded surface and subsurface horizons. Spatial variability accounted for less than 10% of the variation in denitrification rates, while soil horizon amounted to about 50%. Within the soil columns, the relative NO−3 concentration decreased rapidly with increasing temperature in the surface horizons but much less so in the subsurface horizon. For the surface horizons, incubated at the higher temperatures, NO−3 concentration in the effluent was very low, suggesting that denitrification may have been limited by NO−3 availability. The denitrification potential for the surface horizons was very high, related in part to the high levels of organic carbon present in those horizons.

Copper availability in two soils amended with eleven annual applications of copper‐enriched hog manure

Abstract Relatively high amounts of Cu are found in manure of hogs (Sus scrofa domesticus) maintained on diets containing growth‐stimulating levels of Cu. While disposal of Cu‐enriched hog manure through repeated long‐term application to agricultural land is commonly practiced, concern exists regarding Cu availability in these soils. Field studies were conducted on a Bertie fine sandy loam (Aquic Hapludults) and a Starr‐Dyke clay loam (Fluventic Dystochrepts‐Typic Rhodudults), located in the Coastal Plain and Piedmont regions of Virginia. The objective was to examine the effects of long‐term Cu application on corn (Zea mays L.) growth and to ascertain the Cu sorption capacity of these soils. Field plots were treated with Cu‐enriched hog manure or CUSO4 (on an equivalent Cu basis) annually. Manure amendments totaled about 240 t ha‐1 (dry weight) over an 11 yr period (1978 through 1989). The manure averaged 1300 mg Cu kg‐1 (dry weight) over this time period totaling 340 kg Cu ha‐1. Sorption isotherms were d...

EVALUATING ENVIRONMENTAL HAZARDS OF LAND APPLYING COMPOSTED DIAZINON USING EARTHWORM BIOASSAYS

Environmental hazards resulting from land application of composted pesticide residue have not been rigorously evaluated. This study was conducted to examine the toxicity of a composted pesticide residue using earthworms (Eisenia foetida Savigny) as a microinvertebrate model in a soil bioassay system. Diazinon, which was used in these experiments as a test pesticide, was removed from simulated rinsate (wastewater) by sorption onto peat moss. Following the rinsate clean-up phase, diazinon-laden peat moss was placed into bioreactors and composted for either 30 or 60 days. Earthworms were then exposed to soil amended with the composted material. Mortality and symptomatic effects characteristic of acetylcholinesterase inhibition, including weight loss, reduced burying ability and curling, occurred in earthworms exposed to soil amended with either uncomposted or 30-day composted diazinon, but not in those exposed to soil amended with 60-day composted diazinon. The amount of solvent-extractable diazinon from compost was not directly related to acute earthworm toxicity based on the selected criteria. These results indicated a reduction in diazinon bioavailability during latter 30 d of composting that did not correspond to a reduction in solvent-extractable diazinon concentrations. Measuring symptomatic effects of xenobiotics as described in this study may increase the sensitivity and diagnostic ability of earthworm bioassays.

Application of solid state fermentation techniques to dispose of chlorpyrifos and metolachlor

Abstract Small-scale farm operators have a pressing need for methods to dispose of unused concentrated and dilute formulated pesticide suspensions or solutions such as rinsate. The suitability of solid state fermentation (SSF) techniques to dispose of chlorpyrifos and metolachlor was evaluated. Pesticides were added to bioreactors containing either sphagnum peat moss, steam-exploded wood (SEW), or a wheat straw-horse manure mixture. Sorbent material was sampled periodically to determine pesticide content. In peat, SEW, and wheat straw-horse manure filled bioreactors containing chlorpyrifos at a loading rate of 1.0 g kg −1 (dry wt. basis), solvent extractable levels of pesticide decreased to 0.5, 24, and 0.6% of starting levels in 290, 270, and 290 days of bioreactor operation, respectively. In peat, SEW, and wheat straw-horse manure filled bioreactors containing metolachlor at a loading time of 2 g kg −1 (dry wt. basis), solvent extractable levels of pesticide decreased to 23, 49, and 0.3% of starting levels within 315, 315, and 120 days of reactor operation, respectively. Soil column leaching studies were conducted using peat and wheat straw-horse manure sorbents following bioreactor shutdown, to assess the potential environmental hazard of land applying spent sorbent materials. The amount of chlorpyrifos and metolachlor leached from peat was greater than that from wheat straw-horse manure. Based on leachability studies, the wheat straw-horse manure was superior to peat as a disposal matrix material. The use of SSF techniques to dispose of pesticide waste may prove a viable alternative to other disposal methods that are either too expensive or technically sophisticated.

Fate of atrazine and chlorpyrifos during solid state fermentation : Examination of processes

Abstract Solid state fermentation (SSF) was investigated as a means to dispose of two commonly used pesticides, chlorpyrifos (O, O‐diethyl O‐(3,5,6‐trichloro‐2‐pyridyl) phosphorothioate) and atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine). SSF experiments were carried out in bench‐scale bioreaetors (equipped with CO2 and volatile organic traps) containing a mixture of lignocellulosic materials and a radiolabeled pesticide. Ethyl acetate‐extractable, alkali soluble, and alkali insoluble fractions were evaluated for radioactivity following a 60‐d incubation period at 40°C. The majority of the [2, 6‐pyridyl‐14C]chlorpyrifos was associated with the ethyl acetate extract (about 74%), 17% was trapped as organic volatiles by polyurethane foam traps and < 0.5% of the chlorpyrifos was mineralized to CO2. Only small amounts of the radioactivity were associated with alkali soluble (0.0003%) and alkali insoluble (0.3%) fractions. In the [14C‐U‐ring] atrazine bioreactors, very little of the radioactivity volatilized (<0.5%) and less than 0.5% was mineralized to CO2. Approximately 57% of the applied radioactivity was associated with the ethyl acetate extract while 9% and 24% of the radioactivity was associated with the alkali soluble (humic and fulvic acids) and alkali insoluble fractions, respectively. Possible reaction mechanisms by which covalent bonds could be formed between atrazine (or metabolites) and humic substances were investigated. The issue of bound atrazine residue (alkali soluble fraction) was at least partially resolved. Oxidative coupling experiments revealed that formation of covalent bond linkages between amino substituent groups of atrazine residue and humic substances is highly unlikely.

The fate of 14C-diazinon in compost, compost-amended soil, and uptake by earthworms

A process for disposing of pesticide rinsates using sorption onto organic matter followed by composting is being evaluated. As a part of this evaluation process, we have studied the bioavailability of composted Δ‐2‐14C‐diazinon and its degradation products to earthworms (Eisenia foetida Savigny) in 30 and 60 d compost amended soil. After 60 d of composting there was considerable degradation of diazinon (95%) and a corresponding increase in the primary hydrolysis product, 2‐isopropyl‐4‐methyl‐6‐hydroxypyrimidine (IMHP) as determined by high performance thin layer chromatography (HPTLC). Approximately 50% of the radioactivity became incorporated into the non‐extractable fractions associated with composted organic matter with no measurable amounts of 14CO2 produced during the 60‐day composting period. Following addition of the composted materials to soil, diazinon leading to 50% mortality after 14 d of exposure; continued to slowly degrade and become increasingly sorbed/entrapped within the soil‐compost matrix. Soil amended with 30‐d composted diazinon was toxic to earthworms whereas, no mortality was observed in those earthworms exposed to the 60‐d composted diazinon. However, earthworms exposed to 30‐d and 60‐d composted diazinon were found to have similar levels of radioactivity in their tissues. The majority of the radioactivity in earthworms exposed 60‐d composted diazinon was either unextractably bound within the earthworm tissue or was not acetone soluble. Most of the radioactivity that could be extracted with acetone was not separated by the two HPTLC methods we used. This study demonstrates that composting high concentrations of diazinon can greatly reduce toxicity and the amount of diazinon that is bioavailable to a representative soil macroinvertebrate (E. foetida).

Evaluation of economical sorbents for removal of metolachlor from rinsate wastewater

Abstract Small-scale farm operators and applicators are in urgent need of inexpensive user-friendly methods to decontaminate dilute formulated pesticide solutions such as rinsate solutions. One requisite to development of such methods is the identification and selection of inexpensive effective sorbents. Three different sorbents (rubber, sphagnum peat moss, and steam-exploded wood [SEW]) were evaluated for their ability to remove analytical grade and formulated metolachlor (as Dual 8E, an emulsifiable concentrate) from an aqueous phase, using the batch equilibrium method. Rubber proved to have the greatest sorptive capability, followed by peat and SEW. At the highest concentration of (formulated) pesticide tested (400 mg L −1 ), rubber was 85% efficient in removing metolachlor from solution, while peat and SEW were 71% and 55% efficient in metolachlor removal. The presence of surfactants in the formulated pesticide appeared to decrease metolachlor sorption. The addition of Ca(OH) 2 , a demulsifying agent, to the formulated pesticide suspensions (400 mg L −1 ) decreased the sorption capability of peat and SEW by 31% and 20%, respectively. Calcium hydroxide treatment increased sorption capability of rubber by 3%. The combination of Ca(OH) 2 and rubber proved to be the superior treatment in terms of removing formulated metolachlor from solution.

Evaluation of synthetic adsorbents for cleanup of herbicide-laden wastewater

Abstract Small-and large-scale farm operators and applicators urgently need user-friendly and cost-effective on-site methods to treat dilute-formulated herbicide-laden wastewater (i.e., rinsate). In this study, we investigated solvent-regenerable synthetic adsorbents, Ambersorb® 563 adsorbent, Ambersorb 572 adsorbent, and Ambersorb 575 adsorbent, as alternatives to activated carbon (Filtrasorb ® 400) for cleanup of water containing Dual 8E (a.i., metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide]) or Banvel 4L (a.i., dicamba [3,6-dichloro-2-methoxybenzoic acid]). Batch-type adsorption experiments were conducted to compare adsorptive capacities of the various adsorbents. Adsorption maxima, obtained from adsorption isotherms, indicated that of the Ambersorb adsorbents tested, Ambersorb 572 adsorbent generally exhibited the highest adsorptive capacities for the herbicides tested and was comparable to Filtrasorb 400. Solvent (methanol) regenerability studies demonstrated that herbicide was readily recovered from Ambersorb 572 adsorbent and Filtrasorb 400. In general, metolachlor was more readily recoverable than dicamba. In fixed-bed column studies, Ambersorb 572 adsorbent exhibited twice the adsorptive capacity of Filtrasorb 400. Fixed-bed columns were more effective in removing metolachlor from herbicide containing water regardless of the adsorbent used. Multicycling of Ambersorb 572 adsorbent resulted in 30% loss of adsorptive capacity for dicamba as Banvel 4L and no loss of adsorptive capacity for metolachlor as Dual 8E. Working capacity was reached after three adsorption-regeneration cycles. Fixed-bed columns packed with solvent-regenerable adsorbents may prove useful as part of an on-site wastewater disposal system.