Analysis of Gasses Emitted from Lignosulfonates Applied as Road Dust Suppressants.

Lignosulfonates have long been applied to roads to control dust and provide surface stabilization. These products are typically applied as dilute solutions that permeate into the road base. During the application and for some time after, there is a certain aroma associated with the road. This lignosulfonate-derived odor has sometimes been described as a burnt sugar type smell.

A study into the chemical nature of the gasses responsible for this odor has recently been completed at the University of Washington. The goal of this study was to identify the various volatile chemicals emitted by the lignosulfonates and in particular to verify that sulfur dioxide was not released. The results of this investigation are published in the Journal of Environmental Management 1.

A special chamber was constructed to mimic a road surface. Lignosulfonates were applied to three different soils at typical dust control treatment levels. The soil types tested included a sandy to loamy Western Washington soil (pH 4.59), a clay soil from Northern California (pH 5.2) and an extremely rocky, sandy clay soil (pH 8.3) also from Northern California. Gasses emitted over a one week time period from the soil/lignosulfonates were continuously swept out of the chamber and trapped for analysis. Several commercial lignosulfonate products representing a wide range of chemical and physical characteristics were tested.

An important finding from this study was that sulfur dioxide was not detected 2 in the emissions from any of the commercial lignosulfonate products applied to these three soil types. Both the pH and the binding capacity of the soil inhibited the release of sulfur dioxide. Only when the lignosulfonate/soil system was acidified to extremely low pH conditions (pH<1) was any sulfur dioxide detected. These conditions are only found under unusual conditions such as with mine tailings.

The aroma of lignosulfonates was found to be due to a small number of volatile chemicals present in very trace amounts -- most below 10-20 micrograms per liter . The majorities of these types of chemicals are removed from the lignosulfonates by processing steps such as evaporation or spray drying prior to sale. In all the samples, furfural (2-furancarboxaldehyde) proved to be the most abundant aroma chemical present. This material is produced from the high temperature breakdown of the sugar, xylose. Furfural is also found in the aromas of other natural products such as fruits, tea, and coffee. Also identified in the emissions in amounts far less than furfural were a variety of furfural type compounds, acetic acid , and ethanol.

The conclusion reached from this study is that there are no health issues associated with the types and amounts of aroma chemicals found in lignosulfonates. Overall, the aroma is not all that much different from what is found with other natural products…. such as brewing coffee and baking bread.

1 Nelson, Julie, Northey, Robert, Gaseous Emissions from Lignosulfonates in Dust Abatement Applications, Journal of Environmental Management 73 (2004) 333-338
2 The detection limit for this system was 0.01 mg SO 2/g applied lignosulfonate solids.