In Situ Investigation the Photolysis of the PAHs Adsorbed on Mangrove Leaf Surfaces by Synchronous Solid Surface Fluorimetry

Abstract

An established synchronous solid surface fluorimetry (S-SSF) was utilized for in situ study the photolysis processes of anthracene (An) and pyrene (Py) adsorbed on the leaf surfaces of Kandelia obovata seedlings (Ko) and Aegiceras corniculata (L.) Blanco seedlings (Ac). Experimental results demonstrated that the photolysis of An and Py adsorbed on the leaf surfaces of two mangrove species under the laboratory conditions, followed first-order kinetics with their photolysis rates in the order of Ac>Ko. In addition, with the same amount of substances, the photolysis rate of An adsorbed on the same mangrove leaf surfaces was much faster than the adsorbed Py. In order to investigate further, the photolysis processes of An and Py in water were also studied for comparison. And the photolysis of An and Py in water also followed first-order kinetics. Moreover, for the same initial amount, the photolysis rate of the PAH in water was faster than that adsorbed on the leaf surfaces of two mangrove species. Therefore, photochemical behaviors of PAHs were dependent not only on their molecular structures but also the physical-chemical properties of the substrates on which they are adsorbed.

Direct Observation of the Photodegradation of Anthracene and Pyrene Adsorbed onto Mangrove Leaves

“…adata from our previous studies [30].bthe value of ln( F 0 / F t ).cthe illumination time of ANT adsorbed onto mangrove leaves.…”

“…According to our previous studies and others, the mature viviparous hypocotyls of Ko when off the trees could be collected for cultivation, and the non-viviparous seedlings of Ac who are least one-year old could be taken away from the forest and cultivated for further experiments [30] , [31] . Therefore, mature mangrove hypocotyls of Ko and 1-year-old Ac seedlings were collected at the Longhai mangrove reserve in Zhangzhou, Fujian, China (longitude: 24°29′3″, latitude: 118°5′59″, altitude: 0 m above sea level).…”

“…After the collection of the leaves, experiments were carried out as soon as possible. Pretreatment of the leaves followed the steps established in our previous studies [29] , [30] , [31] . The picked fresh mangrove leaves were carefully rinsed with distilled water to remove surface silt.…”

“…Thus, the optimized irradiation of the ANT and PYR adsorbed on the leaves of Ko and Ac should be set at the same sequence. That is the optimized irradiation time for the PAHs adsorbed onto the Kc leaves was set at 0 min, 1 min, 3 min, 7 min, 13 min, 20 min, 30 min, 45 min, 60 min, 80 min, and 100 min, 120 min and 140 min, respectively, and the optimized irradiation time for the adsorbed PAHs on the Ac leaves was set at 0 min, 1 min, 3 min, 7 min, 13 min, 20 min, 30 min, 45 min, 60 min, 80 min, 100 min, 120 min and 140 min, respectively [30] . Fluorescence spectra were obtained using the following instrumental setting: excitation and emission slits of 20 and 10 nm, respectively; scan speed of 120 nm min −1 ; PMT voltage of 600 V; and the constant wavelength difference (Δ λ ) was set at 38 nm.…”

“…Our previous research sought to elucidate the environmental behaviors of PAHs adsorbed onto mangrove leaves using an established synchronous fluorimetry combined with a fluorescence spectrophotometer and an optical fiber to directly detect PYR and ANT adsorbed onto mangrove leaves [29] . The photodegradation of PYR and ANT adsorbed onto the leaves of two mangrove species as single component have also been studied in our laboratory [30] . However, the environmental behaviors of PAHs are very complex in the field.…”