Monocrotophos (MCP) is an organophosphate insecticide that has been found as a pollutant in aqueous environments. The sonolytic, photocatalytic and sonophotocatalytic degradation of MCP in the presence of homogeneous (Fe3+) and heterogeneous photocatalysts (TiO2) were studied. The photocatalytic degradation rate using TiO2 was found to be lower than that of sonolysis alone due to the interference of phosphate ions formed as an intermediate product. On the other hand, a 15 fold enhancement in the degradation rate was found when photolysis was carried out in the presence of Fe3+ compared to the rate observed with photolysis alone. The combination of sonolysis and photocatalysis (using either TiO2 or Fe3+) showed a detrimental effect. Synergy indices of 0.62 and 0.87 were found for the sonophotocatalytic degradation of MCP in the presence of TiO2 and Fe3+, respectively. Total organic carbon (TOC) analysis was carried out to study the extent of mineralization of MCP. It was found that the mineralization process was additive for both TiO2 and Fe3+ sonophotocatalysis. HPLC and electrospray mass spectrometry (ESMS) techniques were employed for the identification of the degradation intermediates. The sonication of MCP led to the formation of dimethyl phosphate, dimethylphosphonate, 3-hydroxy 2-buteneamide and N-methyl 3-oxobutanamide as the intermediate products. (C) 2010 Elsevier B.V. All rights reserved.