EDB was previously used as a soil fumigant and as a leaded gasoline additive while 1,2-DCA is currently produced in large quantities as a commercial chemical.. EDB is not typically found
Introduction
This document reviews the environmental fate literature for ethylene dibromide (EDB) and 1,2-dichloroethane (1,2-DCA), two structurally similar compounds Despite their names suggesting different structures, both EDB and 1,2-DCA lack a double bond and differ only in their substituents, with EDB containing bromine and 1,2-DCA containing chlorine.
Table 1 A comparison of structure and nomenclature for the lead scavengers ethylene dibromide and 1,2-DCA
Chemical name used in report EDB 1,2-DCA
CAS-9CI name Ethane, 1,2-dibromo- Ethane, 1,2-dichloro-
Synonyms Ethylene dibromide Ethylene dichloride
EDB was historically utilized as a soil fumigant and a leaded gasoline additive, but its use is now prohibited in the U.S In contrast, 1,2-DCA is produced in significant quantities, with nearly 8.2 billion kilograms manufactured in the mid-1990s, primarily serving as a chemical intermediate (over 96% of its use) The current detection of 1,2-DCA in air, surface water, and groundwater is largely due to its high production volume, while EDB is rarely found in recent environmental samples.
EPA However, it has been reported in groundwater and soil samples affected by historical uses
This article reviews environmental fate data for EDB and 1,2-DCA, including monitoring data from sites of direct release and larger studies where concentrations are not linked to a single source Section II outlines the literature search process, while Sections III and IV present environmental information for EDB and 1,2-DCA, respectively Both sections discuss transport processes, abiotic and biotic transformations, and monitoring data Although EDB and 1,2-DCA are analyzed separately, their environmental processes are expected to be similar Notably, the physical trapping of EDB in soil has been extensively studied due to its use as a soil fumigant, suggesting that similar mechanisms may apply to 1,2-DCA based on their structural similarities Readers are directed to the relevant sections for original data.
Technical Approach
The literature search utilized the SRC's Environmental Fate Data Base (EFDB), DATALOG, and BIOLOG to gather information on abiotic and biotic transformation processes, environmental transport, and physical/chemical properties DATALOG offers a citation index organized by environmental processes such as adsorption and biodegradation, along with studies on physical/chemical properties and environmental concentrations across various media Since DATALOG focuses on mixed culture studies, BIOLOG was consulted for insights on pure culture biodegradation Both EDB and 1,2-DCA were extensively covered in the literature Additionally, a Chemical Abstracts search was performed using degradation and media keywords for citations from the year 2000 onward.
SRC conducted comprehensive literature searches, including references from the Request for Proposal (RFP) and the reference sections of identified papers, which effectively uncovered recent articles from lesser-known sources like conference proceedings Online searches via GOOGLE were employed to find unpublished field study data and recent monitoring information Notable articles by Falta and Bulsara (2004), Burton (2005b), and Miner (2005) were discovered through this method, along with relevant presentations from the Annual Clemson University Hydrogeology Symposium and government resources such as ATSDR Health assessments and Superfund site Record of Decision documents.
Historical and Current Use Patterns
EDB, first produced in 1923, has historically been used as a soil fumigant and an additive in leaded gasoline and aviation fuel It has also served as an intermediate in the synthesis of dyes and pharmaceuticals, as well as a solvent for resins, gums, and waxes Currently, EDB is primarily utilized as a chemical intermediate in the production of vinyl bromide, a flame retardant for modacrylic fibers, and as a nonflammable solvent Additionally, it is employed in the treatment of felled logs to combat bark beetles and control wax moths in beehives, and as a lead scavenger in leaded fuels for off-road applications, including aircraft, racing cars, and marine engines.
Monitoring data reveal that very low concentrations of EDB are present in ocean water and air, indicating that EDB may naturally form in ocean environments, potentially due to the growth of macroalgae.
U.S production of EDB reached its peak in 1974 at 150.9 million kilograms, but by 1983, it had declined to 70.5 million kilograms This reduction was primarily due to the cancellation of EDB's pesticide registration in 1983/1984 and the implementation of catalytic converters in passenger vehicles starting in 1975, which was a response to stricter emission standards Additionally, the phase-out of leaded gasoline began in 1978 Inventory Update Reporting (IUR) data shows EDB production volumes for various years: over 45.5 million to 227 million kilograms in 1986, over 22.7 million to 45.5 million kilograms in 1990, over 4.5 million to 22.7 million kilograms in 1994, and both 1998 and 2004 recorded production of over 0.45 million to 4.5 million kilograms.
Figure 1 Annual U.S production of EDB from 1969 to 1983 (U.S ITC, 1970–1984)
EDB, registered as a pesticide in 1948, was primarily used to control soil nematodes and sold as a liquid with petroleum solvents Its applications included spot fumigations in grain milling machinery, post-harvest grain fumigation, and pest control in fruits and vegetables, as well as minor uses against various pests like mountain pine bark beetles and termites However, the discovery of EDB in stored grain and well water in 1983 led to an EPA ban on its agricultural uses, citing concerns about groundwater contamination and leaching Consequently, EDB's registration for soil fumigation was canceled in 1983, followed by the cancellation of its use on grains and grain milling machinery in 1984.
In 1975, approximately 3–4% of the total 1975 EDB production was used as a pesticide (U.S EPA,
By 1983, approximately 10 million kg of the active ingredient EDB was applied to around 400,000 hectares of various crops in the U.S., accounting for 11% of the total EDB production that year In stark contrast, an estimated 111 million kg of EDB was utilized annually as a lead scavenger in leaded gasoline and aviation fuel during the same period.
Leaded gasoline was commercially available starting in 1923, with the addition of ethylene dibromide (EDB) in 1925 to enhance performance (Burton, 2005a) EDB and 1,2-dichloroethane (1,2-DCA) were incorporated into the fuel to mitigate the accumulation of solid lead oxides on spark plugs and exhaust valves in piston engines (Burton, 2005b) During combustion, volatile lead bromide and lead chloride were emitted into the atmosphere The concentration of EDB in leaded gasoline varies based on the lead content, with fuels from 1942 to the present containing 1.0 mole of 1,2-DCA and 0.5 mole of EDB per mole of alkyl.
Ethylene dibromide production (million kg/yr)
Before 1942, different molar ratios of ethylene dibromide (EDB) to 1,2-dichloroethane (1,2-DCA) were utilized, with aviation fuel containing solely EDB at a ratio of 1.0 mole EDB per mole of alkyl lead, resulting in aviation fuel having twice the amount of EDB compared to leaded gasoline.
Lead concentrations in gasoline have fluctuated significantly since the 1920s when lead was found to reduce engine spark knock The federal government initially set a maximum limit of 3.17 g lead/gallon in 1926, which was raised to 4.23 g lead/gallon in 1959 to accommodate higher compression ratios and octane needs In the late 1960s, average lead levels peaked at 3.0 g lead/gallon for premium and 2.5 g lead/gallon for regular gasoline However, by the 1970s, advancements in refining processes led to higher octane gasoline, and the U.S EPA implemented regulations to systematically reduce lead concentrations in gasoline By 1979, the average lead content for large refiners had significantly decreased.
In 1985, a maximum lead limit of 0.5 g per gallon was established for all leaded gasoline produced by refineries generating over 50,000 barrels daily, while small refiners had a limit of 2.65 g per gallon Following several adjustments, by 1988, the average lead content in U.S leaded gasoline was reduced to 0.1 g per gallon.
In 1995, leaded fuel constituted just 0.6% of total gasoline sales in the U.S The sale of leaded fuel for on-road vehicles was prohibited in 1996, but it remains permissible for off-road applications such as aircraft, racing cars, farm equipment, and marine engines Notably, leaded aviation gasoline products like Avgas 80, Avgas 100, and Avgas 100LL (low lead) still contain EDB Among these, Avgas 100LL is the most widely used aviation fuel for spark-ignition internal combustion engines, particularly in single piston airplanes.
The TEL-CB tetraethyl lead package produced by Ethyl Corporation for leaded fuels consists of 61.49% tetraethyllead, 17.86% EDB, and 18.81% 1,2-DCA, resembling the classic ethyl fluid formulation Additionally, the TEL-B package contains 61.49% tetraethyllead and 35.73% EDB, similar to the formulation used in Avgas.
Physical Properties
Table 2 outlines the physical and chemical properties of EDB, highlighting its high vapor pressure and water solubility These characteristics suggest that EDB is likely to volatilize in dry soils, which supports its application as a soil fumigant Additionally, EDB's Henry’s Law constant indicates its tendency to volatilize easily from water surfaces.
EDB is soluble in various organic solvents and, when released into the environment within a fuel mixture, can migrate with light non-aqueous phase liquids (LNAPL) through the vadose zone to groundwater The dissolution behavior of EDB differs when it is part of a gasoline mixture compared to when it is a pure compound In the case of a pure compound like EDB, the water-phase concentrations at the NAPL-water interface reach the solubility limit Conversely, for EDB in a gasoline mixture, the maximum concentration in the water phase is determined by its effective solubility, which can be expressed as a retardation coefficient in a saturated soil matrix.
In soil the retardation coefficient, R i , is: w i oc oc s w i oc oc s w i
With an immobile residual oil phase (gasoline) present, based on presumed ideal Raoult’s law partitioning w o i i o o w i oc oc s w o i i o o i oc oc s w i
Equivalently, for a measured gasoline to water partition coefficient
( ) w i gw o o w i oc oc s w i gw o o i oc oc s w i
The volumetric moisture fraction in the soil matrix, denoted as \$\theta_w\$ (cm³-water/cm³-soil), corresponds to the total soil porosity in saturated conditions The dry bulk density of the soil is represented by \$\rho_s\$ (g-soil/cm³-soil), while the mass fraction of organic carbon in the soil is indicated by \$f_{oc}\$ (g-oc/g-soil) Additionally, the chemical-specific organic carbon-water partition coefficient is expressed as \$K_{oc,i}\$ (cm³-water/g-oc) The molecular weight of the chemical is denoted as \$MW_i\$, and \$S_i\$ represents the pure chemical aqueous solubility limit.
In cases where the chemical of interest constitutes a small portion of the total residual phase, the values of $\theta_o$ (cm³-oil/cm³-soil), $\rho_o$ (g-oil/cm³-oil), and $MW_o$—which depends on the composition of the oil mixture—remain relatively constant Consequently, the factor $R_i$ becomes independent of the overall oil mixture concentration in the soil.
The gasoline to water partition coefficient can be estimated from the octanol to water partition coefficient as: o ol oc ow gw MW
The gasoline-water partition coefficient of EDBs indicates that they dissolve more quickly into groundwater than benzene, which has a partition coefficient of 350 Research by Pignatello and Cohen (1990) suggests that groundwater in contact with gasoline LNAPL at lead levels from 1990 would contain around 80 μg/L of EDB.
(2004b), however, reported a potential maximum concentration of 1900 μg/L for EDB near a residual or
The source of LNAPL gasoline is identified through the gasoline:water partition coefficient of EDB When EDB is released, either independently or as part of a grain bin fumigant spill, it may be mixed with substances such as carbon tetrachloride.
1,2-Dichloroethane (1,2-DCA) is anticipated to migrate through the vadose zone to groundwater as a dense non-aqueous phase liquid (DNAPL) due to its higher density than water Once dissolved in groundwater, 1,2-DCA does not significantly alter the water's density, allowing it to move along with the primary flow of groundwater (Pignatello and Cohen, 1990).
Table 2 Physical/chemical properties for EDB
Physical description Colorless, heavy non-flammable liquid U.S EPA (1977) Molecular weight 187.86 g/mol
Octanol: miscible Organic solvents: miscible
Horvath et al (1999) Johns (1976) Alexeeff et al (1990) Vapor pressure 11.2 mm Hg at 25 °C Daubert and Danner (1985)
Octanol-water partition coefficient 91.2 Hansch et al (1995)
Henry’s Law constant 6.5x10 -4 atm-m 3 /mol at 25 °C
Falta and Bulsara (2004) Gasoline-water partition coefficient
Specific gravity (liquid) 2.179 at 25 °C Alexeeff et al (1990)
Specific gravity (vapor) 6.5 at 25 °C Alexeeff et al (1990)
Equilibrium aqueous concentration 1900 μg/L Henderson (2005) Diffusion coefficient in dry air 0.0813 cm 2 /sec (20 °C)
0.0708 cm 2 /sec (0 °C) Pignatello and Cohen (1990) Diffusion coefficient in water 1.0x10 -5 cm 2 /sec (25 °C, estimated) Pignatello and Cohen (1990)
Density 2.701 at 25 °C van Agteren et al (1998)
Vapor density relative to air 6.1; density of EDB saturated air is
Heat of vaporization +53 cal/gm at 25 °C U.S EPA (1977)
Percent in saturated air At saturation, the concentration of
EDB is 1.3% by volume at 25 °C U.S EPA (1977) Conversion factors 1 ppm = 7.68 mg/m 3 in air
Transport Processes
Transport from Water Surfaces
The volatilization of EDB from water occurs rapidly upon release, with overall mass transfer coefficients influenced by wind speed (Rathbun and Tai, 1987) The resistance of EDB to volatilization is significantly affected by both gas-film and liquid film coefficients.
(Rathbun and Tai, 1986) Lyman et al (1982) estimated liquid- and gas-phase exchange coefficients of
The estimated volatilization half-life is 4 hours, calculated using a wind speed of 3 m/sec and a mass transfer coefficient of 11.4 cm/hr The relevant measurements include 16 and 1400 cm/hr for water speed.
Lyman et al (1982) reported a gas-film coefficient of 1 m/sec for the volatilization of EDB from water Rathbun and Tai (1987) measured gas-film coefficients of 286 m/d (1192 cm/hr) and 533 m/d (2221 cm/hr) for low (0.1 m/sec) and high (2.0 m/sec) wind speeds, respectively, at a temperature of 25 °C.
(1993) measured mass-transfer coefficients of EDB at varying impeller speeds (150 to 500 rpm) Mass transfer coefficients of 0.14, 0.53, 1.05, and 1.30 hr -1 were reported for 150, 200, 400, and 500 rpm,
Hsieh et al (1993) and Rathbun and Tai (1987) reported gas film constants of 0.68 and 0.410, respectively The water-film mass-transfer coefficient for the volatilization of EDB is 63.3% of the reaeration coefficient for oxygen absorption in a stream, as indicated by a water-film reference substance parameter of 0.633 (Rathbun, 1998) Additionally, an air-film reference substance parameter of 0.393 suggests that the air-film mass-transfer coefficient for EDB volatilization from a stream is 39.3% of the mass transfer coefficient for water evaporation (Rathbun, 1998).
Mackay and Yeun (1983) conducted measurements of EDB volatilization rates in a wind-wave tank, finding overall mass transfer coefficients of 23.6, 45.3, 54.7, and 77.2 x10 -6 m/sec at wind speeds of 5.96, 8.57, 10.31, and 77.2 m/s, respectively They calculated a water evaporation half-life of 4.26 hours at a wind speed of 8.57 m/sec and a depth of 0.61 m, noting that laboratory-derived mass transfer coefficients tend to be higher than those observed in natural environments Additionally, Chiou et al (1980) reported an evaporation half-life of 6.4 minutes for EDB in water at 23.1°C, with an initial concentration of 0.1 ppm, a depth of 1.6 cm, and a stirring speed of 100 rpm In still air, the evaporation rate of EDB from water was measured at 1.24x10 -5 g/cm 2 -sec Volatilization data from spill sites for 1,2-DCA further confirm the rapid volatilization of small molecules from water surfaces.
Transport in Soil
The movement of chemicals in the vadose zone is influenced by transport and adsorption processes EDB can exist in various forms, including dissolved in solution, vapor, adsorbed to soil, free NAPL, or residual NAPL, depending on the release scenario Dissolved EDB migrates to the water table with infiltrating water through advection, while vapor-phase EDB diffuses through the soil EDB in LNAPL or DNAPL primarily moves downward due to gravitational and capillary forces A small NAPL release may be contained by the soil, but a larger release can reach the groundwater table, where LNAPL accumulates and DNAPL continues to migrate until it hits a confining layer The movement of NAPL is affected by soil porosity, permeability, and capillary pressure, and it can become trapped in the soil matrix, leaving residual NAPL that may serve as a long-term source of soluble components to the environment.
Research on the sorption of vapor-phase EDB to soil has been conducted by Thomason and McKenry (1974) and Sawhney and Gent (1990) In their soil chamber studies, EDB was injected into dry montmorillonite silty clay loam soil at a depth of 30.5 cm with an application rate of 47 L/ha, resulting in a vapor-phase concentration of 4.5x10⁻⁷ moles/L (0.05 ppm) at 90 cm depth within 7 days Additionally, in sandy loam soil, approximately 1% of the EDB was lost to the atmosphere after 14 days, with expectations of higher losses under field conditions Notably, the findings from Thomason and McKenry (1974) contrast with volatilization half-lives of 0.4 and 3.4 days at 1 and 10 cm depths, respectively, as estimated by Jury et al (1984).
The sorptive capacity of vapor-phase EDB was evaluated in two soil types, sandy loam and silty clay loam, under varying temperature and soil moisture conditions.
At moisture tensions exceeding 15 bars, both sandy loam and silty clay loam soils exhibited significantly increased sorptive capacities, with sandy loam showing greater capacity Soil incubated at 15 °C demonstrated higher sorptive capacity compared to that at 25 °C A mass balance analysis at 15 °C revealed that by day 7 post-treatment, approximately 24% of the initially-added EDB was found in the soil water phase, while 24% remained unaccounted for, and 50% was in the soil particle phase, with 2% in the soil vapor phase By day 15, the distribution changed to 20% in the soil water phase, 40% unaccounted for, 38% in the soil particle phase, and 1% lost to the atmosphere Additionally, Sawhney and Gent (1990) found that the vapor-phase sorption of EDB to various clay minerals was initially high but slowed over time, with 3% to 9% EDB by weight sorbed to different minerals, although sorption was not correlated with BET surface areas EDB desorption from the columns also showed a rapid initial rate that decreased as the study progressed.
Results from early studies show linear sorption isotherms for aqueous-phase EDB (Call, 1957; Phillips,
Phillips (1964) found that the sorption of EDB to various soil types, including sand loam, silt loam, and peaty soil, exhibited a linear relationship The composition of these soils varied in terms of coarse sand, fine sand, silt, clay, and organic matter Additionally, the moisture content significantly influences EDB sorption, with drier soils demonstrating higher adsorption levels This effect is observed at a moisture transition point between 5% and 20% water relative to the dry weight of the soil (Pignatello and Cohen, 1990).
Recent studies indicate that the sorption of EDB is influenced by the presence of other compounds When measured as a single solute, EDB exhibited a Kp value of 0.4808 across concentrations of 32 to 1750 μg/L However, in the presence of competing compounds such as chloroform, chlorodibromomethane, bromoform, trichloroethene, and tetrachloroethene, the sorption of EDB significantly decreased Specifically, the Kp value dropped from 0.77 to 0.25, a reduction by a factor of 3.1, when trichloroethene concentrations ranged from 0 to 120 mg/kg.
(Pignatello, 1990a) In the presence of o-dichlorobenzene, the Kp of EDB decreased by a factor of 1.4 (from 0.77 to 0.55) at sorbed o-dichlorobenzene concentrations of 0 to 240 mg/kg, respectively
Chiou and Kile (1998) investigated the sorption of EDB using peat and mineral soils, revealing that EDB exhibited non-linear sorption at low concentrations but became linear at medium to high concentrations The apparent non-linear sorption capacities were found to be 0.18 mg/g for peat and