Evaluation of pyrene sorption–desorption on tropical soils

• Pyrene sorption was carried out on soils having contrasting physicochemical properties.
• Pyrene sorption was exothermic and soil solution pH had reciprocal effect on it.
• Sorption exhibited distributed reactivity involving several linear and non-linear isotherms.
• Sorption was partly surface adsorption and partly partitioning between phases in soil.
• Higher hysteresis was observed in soils with higher organic matter.

Sorption–desorption processes control soil-pollutant interactions. These processes determine the extent of pyrene transport in soils. Understanding sorption characteristics of pyrene is necessary in ascertaining its fate in soil. Laboratory batch experiments were conducted to study the sorptions–desorption of pyrene on eight soils from varying tropical agro-ecological zones (AEZs). The results showed that pyrene sorptions equilibria were attained within 720 min. Solution pH had a reciprocal effect on pyrene sorptions. Sorption was exothermic and increased with pyrene concentration in solution. The quantities of pyrene sorbed by each soil as well as the hysteresis were proportional to the percentage organic matter, and to some degree, the clay mineralogy. Sorption isotherms showed distributed reactivity involving several linear and non-linear isotherms. The present investigation showed that pyrene is likely to be more available to biota and reach the aquifer faster in low organic matter soils than those with relatively higher organic matter and more so in warmer climes.