Leaching and Acute Toxicity Testing of Chemically Stabilized Gravel Roads

Abstract: The use of chemicals in gravel road stabilization has increased due to growing traffic and their effectiveness in reducing maintenance costs. Most studies, mainly from industry, focus on performance, with limited research on environmental and toxicological effects. This raises concerns about potential toxicity and the leaching of harmful substances into soil and water. With growing concern, this study focused on evaluating the potential for metals leaching and toxicity of chemically stabilized gravel roads through batch leaching tests and acute toxicity tests using the Daphnia magna species, respectively. For this purpose, the gravel samples were collected from the roads in Minnesota before and after chemical stabilization using calcium chloride (CaCl₂), magnesium chloride (MgCl₂), and BaseOne. Comprehensive tests, including pH, electrical conductivity (EC), trace metals concentration, and acute toxicity, were performed on leachates to evaluate environmental risks of stbilized roads.

Results showed that the concentration of metals was within the prescribed limits of threshold by the U.S. EPA water quality criteria. Salt-based stabilizers (CaCl₂ and MgCl₂) increased EC and leachable metals (Ca, K, Mg, Na, Si, B, Cl) after construction. CaCl₂-treated sites had 1,140% higher concentrations of calcium (234.4 mg/L), 641% higher concentration of potassium (12.9 mg/L), and 4,612% higher concentration of chloride (603 mg/L) compared to the values before application. Similarly, the MgCl₂-treated sites had 4,676% higher concentrations of magnesium (149.0 mg/L) and 491% higher concentrations of aluminium (55 µg/L), compared to the values before application. In contrast, the concentrations of metals from the BaseOne-treated sites after application increased less than those of the other stabilizers. The concentrations of calcium increased 4.2% only after application (16.3 mg/L), the concentration of magnesium 3% (3.3 mg/L), and nickel 14% (1.6 µg/L). Daphnia magna tests showed no short-term toxicity. Acute toxicity assessments using Daphnia magna confirmed that none of the stabilizers caused significant short-term mortality, indicating no immediate environmental hazard.