Diclofenac and two of its photooxidation products in the marine environment: Their toxicology and occurrence in Red Sea coastal waters

Direct effects of sunlight irradiation on the photochemical degradation of diclofenac (DCF) has been investigated in coastal Saudi Arabia (Jeddah) under controlled field conditions. Indirect effects from processes like sensitization and photocatalysis were excluded for this study. Photodecomposition of DCF under natural sunlight is essentially identical during summer and winter but slowed down considerably under cloudy conditions. 9H-Carbazole-1-acetic acid (D1) and 8-chloro-9H-carbazole-1-acetic acid (D2) were the main transformation products. When exposed to sunlight under the same conditions, the former acid reacted more slowly than DCF, the latter more rapidly. DCF exhibits antibacterial activity against multidrug-resistant bacteria, the carbazoles do not, and both DCF and the carbazoles are nontoxic to brine shrimp (Artemia salina). Only 9H-carbazole-1-acidic acid expresses antitumor activity against the Lymphoma cell line and Lewis lung carcinoma (LD50 = 0.044 and 0.066 mM, respectively). A new quantitative analytical method was adopted and validated for simultaneous ultra-trace quantification of DCF, D1, and D2 in contaminated surface waters from the Saudi coast of the eastern Red Sea. The analytical method involved solid-phase extraction (on HLB - hydrophilic - lipophilic balanced phases) followed by liquid-chromatographic separation and tandem mass-spectrometric detection and quantification. DCF was found in the concentration up to 26.9 ng/L. Both D1 and D2 were detected at relatively low concentration ranges (up to 3.3 ng/L and 1.9, respectively).