TBT and TPhT persistence in a sludged soil

Area of Science:

• Environmental Chemistry
• Soil Science
• Ecotoxicology

Background:

• Organotin compounds (OTC), including tributyltin (TBT) and triphenyltin (TPhT), are persistent pollutants.
• Sewage sludge application in agriculture can introduce OTC into soil ecosystems.
• Understanding OTC fate and persistence in soil is crucial for environmental risk assessment.

Purpose of the Study:

• To investigate the persistence of TBT and TPhT in soil after application via spiked sewage sludge.
• To evaluate the influence of sludge quantity, OTC concentration, and soil pH on OTC persistence.
• To identify the main degradation products of TBT and TPhT in soil.

Main Methods:

• Soil samples were spiked with urban sludge containing known concentrations of TBT and TPhT.
• Acidic extraction followed by gas chromatography-pulsed flame photometric analysis (GC-PFPD) was used for OTC speciation.
• Leaching tests were performed on spiked sludge and sludged soil to assess sorption and exchangeability.
• TBT and TPhT concentrations and degradation products were monitored over a 2-month period under varying experimental conditions.

Main Results:

• Over 98% of TBT and 90% of TPhT were initially sorbed onto the sludge.
• More than 50% of TBT remained in soil after 2 months, with persistence increasing at concentrations >1000 µg(Sn) kg⁻¹ sludge.
• TPhT degraded more rapidly, with only 20% remaining after 2 months, forming monophenyltin.
• Soil pH significantly affected persistence: higher pH (>7) and OTC concentration (>100 µg(Sn) kg⁻¹) reduced TPhT degradation but enhanced TBT persistence.

Conclusions:

• TBT exhibits greater persistence in soil compared to TPhT, with dibutyltin as its primary degradation product.
• TPhT degrades more readily, yielding monophenyltin, and its persistence is more sensitive to soil pH and concentration.
• Soil pH plays a critical role in OTC persistence, particularly for TPhT, influencing its fate in agricultural soils amended with contaminated sludge.