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Environmental fate & pathways

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AIR COMPARTMENT

According to a model of gas/particle partitioning of semi-volatile organic compounds in the atmosphere 2,4-dinitrophenol, which has a vapour pressure of 1.49 X10-5 mm Hg at 18 °C, is expected to exist as a vapour in the ambient atmosphere. The vapour-phase 2,4-dinitrophenol is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals (SRC).

The detection of 2,4-DNP by GC in particulate matter in air are indirect indications of the presence of these compounds, but the observation that dinitrophenols are found at least partly in the particulate-sorbed state in the air indicates that their bioavailability from air is < 100% (Nojima K, Kawaguchi A, Ohya T, et al. 1983).

Dry and wet deposition of particulate dinitrophenols are the two significant removal processes in the air, (Alber et al. 1989; Cape1 et al. 1991; Levsen et al. 1990). The detection of 2,4-DNP in rain, and snow showed least partial removal of these compounds occurs by physical processes (Alber M, Bîhm HB, Brodesser J, et al. 1989).

Whether vapour-phase dinitrophenols undergo long-distance transport in the atmosphere needs further study.

WATER COMPARTMENT

The environmental transport of dinitrophenols from water by volatilization would not be significant. The high solubility of 2,4-dinitrophenol in water (5600 mg/l at 18 °C) and its presence in solution primarily as an anion, strongly favour a partitioning tendency toward water rather than air. In fact, based on its vapour pressure, water solubility, and presence predominantly in ionic forms in most natural waters (pKa = 4.09 for 2,4-DNP) the volatilization from water to air is not significant and the loss of dinitrophenols from water due to volatilization it can be considered negligible (Callahan MA, Slimak MW, Gabel NW, et al. 1979).

If released into water, 2,4-dinitrophenol may be adsorbed to suspended solids and sediment in the water column based upon the Koc value.

The sorption and subsequent transport of dinitrophenols from water to suspended solids, sediment and soil would be significant in natural waters that are acidic and/or have high organic matter and clay content. It has been studied that organic carbon content, clay content, and pH of soil and sediment influence the amount sorbed (high clay and organic carbon content and low pH) and increase the concentration of the un-ionized form (Kaufman, 1976 and Callahan, 1979).

A study on concentration ranges of 2,4-DNP in the water of an agricultural watershed showed that the transport of 2,4-dinitrophenol to adjacent surface water or land occurs via runoff or as a result of hydrogeological movement of groundwater to surface water from fields where dinitrophenols have been used as pesticides, or other pesticides have been applied (dinitrophenols may also originate as impurities in certain pesticides such as Dinoseb).

SOIL COMPARTMENT

Koc values collected suggest that 2,4-dinitrophenol is expected to have high mobility in soil (Martins JM, Mermoud A: J Contam Hydrol, 1998). Measured Koc values are in the range of 13.5-16.6 and estimated value of 284.3 L/kg (Kow method). Moreover the pKa of 2,4-dinitrophenol is 4.09, which indicates that this compound will exist primarily as an anion in moist soil surfaces and anions are expected to have very high mobility in soils (SRC).

Volatilization of 2,4-dinitrophenol from moist soil surfaces is not expected to be an important fate process (SRC) since the anion will not volatilize and the neutral species has a Henry's Law constant of 8.6X10-8 atm-cu m/mole at 20 °C and a vapour pressure of

1.49 X10-5 mm Hg at 18 °C (Wild and Jones (1992). The possibility of volatilization of phenolic compounds in soil via co-distillation with water has been suggested and release to air via aerosol formation is possible (Kincannon and Lin 1985).

The mobility of dinitrophenols in soils decreases with increase in acidity, clay, low pH and organic matter content. The ionized form is more water soluble and moves faster through soil.

The transport of dinitrophenols from soil to groundwater also may occur via leaching. The amount of DNP leached depends on the dinitrophenol adsorption capability of soils. Adsorption of phenols in soil increases with a decrease in pH and an increase in organic carbon, goethite (one of the most common iron oxides in soil), and clay content (Hudson-Baruth and Seitz 1986; Kaufman 1976; O’Connor et al. 1990; Shea et al. 1983; Stone et al. 1993).