Microparticles and microplastics contamination in African table salts.

The presence of micro/plastic particles has been reported in various seafood products. However, information on microplastics contamination in salts from African continent is very limited. This study analysed 23 brands of table salts from 8 African countries for microplastics using microscopic/spectroscopic techniques. South Africa showed the highest microplastics concentration (0-1.33 ± 0.32 particles/kg), Nigeria, Cameroun, and Ghana (0-0.33 ± 0.38 particles/kg each); characterized as polyvinyl acetate, polypropylene, and polyethylene. Other countries have no detectable microplastics at 0.3 µm filter pore size. To our best knowledge, this is the first study to characterize micro-fibres/plastics in table salts across African countries, confirming that it is an emission source of micro-fibres/plastics into the human food chain, highlighting the overarching need to understand their effects on human health.

Photochemical production and consumption mechanisms of nitric oxide in seawater.

Nitric oxide (NO•) is an active odd-nitrogen species that plays a critical role in determining the levels of ozone (O3) and other nitrogen species in the troposphere. Here, we provide experimental evidence for photochemical formation of NO• in seawater. Photoproduction rates and overall scavenging rate constants were measured by irradiation of surface seawater samples collected from the Seto Inland Sea, Japan. Photoproduction rates of NO• ranged from 8.7 × 10⁻¹² M s⁻¹ to 38.8 × 10⁻¹² M s⁻¹ and scavenging rate constants were 0.05-0.33 s⁻¹. The steady state concentrations of NO• in seawater, which were calculated from the photoproduction rates and scavenging rate constants were in the range 2.4-32 × 10⁻¹¹ M. Estimation from the scavenging rate constant showed that the NO• lifetime in seawater was a few seconds. Our results indicate that nitrite photolysis plays a crucial role in the formation of NO•, even though we cannot exclude minor contributions from other sources. Analysis of filtered and unfiltered seawater samples showed no significant difference in NO• photoformation rates, which suggests a negligible contribution of NO• produced by photobiological processes. Using an estimated value of the Henry's law constant (kH ≈ 0.0019 M atm⁻¹), a supersaturation of surface seawater of 2 to 3 orders of magnitude was estimated. On the basis of the average values of the surface seawater concentration and the atmospheric NO• concentration, a sea-to-air NO• flux was estimated.

Development of an analytical method for nitric oxide radical determination in natural waters.

The measurement of photochemically generated nitric oxide radicals (NO) in natural waters has long been an arduous task because of a lack of simple analytical techniques, even though the environmental significance of this radical is paramount. We have developed a simple analytical method for the determination of photochemically generated NO in natural waters using 4,5-diaminofluorescein (DAF-2) as a probe compound. This method is based on the reaction of photoformed NO with DAF-2 in air-saturated solution to produce a highly fluorescent triazolofluorescein (DAF-2T) product. DAF-2T was determined by using reversed-phase HPLC with fluorescence detection, with excitation and emission wavelengths of 495 and 515 nm, respectively. Under optimum conditions, the calibration curve exhibited linearity in the range of 0.025-10 nM DAF-2T. The coefficients of variance for the measurements of the signal intensities of DAF-2T (from the photolysis of 0.5 microM and 5 microM NO(2)(-) with DAF-2) were less than 5% and 3%, respectively. For a total irradiation time of 30 min, the detection limit of the photoformation rate of NO was 1.65 x 10(-13) M s(-1), defined as 3sigma of the lowest measured DAF-2T concentration (0.025 nM). The proposed method is relatively unaffected by potential interferents in seawater. The method was employed to determine the photoformation rate of NO in the Seto Inland Sea and the Kurose River in Hiroshima Prefecture, Japan. The measured NO photoformation rates in seawater and river water samples ranged from (5.3-32) x 10(-12) M s(-1) and (9.4-300) x 10(-12) M s(-1), respectively.

Application of Fenton reaction for nanomolar determination of hydrogen peroxide in seawater.

A simple and sensitive method for the determination of nanomolar levels of hydrogen peroxide (H(2)O(2)) in seawater has been developed and validated. This method is based on the reduction of H(2)O(2) by ferrous iron in acid solution to yield hydroxyl radical (OH) which reacts with benzene to produce phenol. Phenol is separated from the reaction mixture by reversed phase high performance liquid chromatography and its fluorescence intensity signals were measured at excitation and emission of 270 and 298nm, respectively. Under optimum conditions, the calibration curve exhibited linearity in the range of (0-50)x10(3)nmolL(-1) H(2)O(2). The relative standard deviations for five replicate measurements of 500 and 50nmolL(-1) H(2)O(2) are 1.9 and 2.4%, respectively. The detection limit for H(2)O(2), defined as three times the standard deviation of the lowest standard solution (5nmolL(-1) H(2)O(2)) in seawater is 4nmolL(-1). Interference of nitrite ion (NO(2)(-)) on the fluorescence intensity of phenol was also investigated. The result indicated that the addition of 10micromolL(-1) NO(2)(-) to seawater samples showed no significant interference, although, the addition of 50micromolL(-1) NO(2)(-) to the seawater samples decreases the fluorescence intensity signals of phenol by almost 40%. Intercomparison of this method with well-accepted (p-hydroxyphenyl) acetic acid (POHPAA)-FIA method shows excellent agreement. The proposed method has been applied on-board analysis of H(2)O(2) in Seto Inland seawater samples.