Effect of sampling time on the heavy metal concentrations of brown algae: A bioindicator study on the Arabian Gulf coast.

Macroalgae have often been studied as bioindicators for heavy metal pollution on sea coasts including the Arabian Gulf. On the Arabian Gulf coasts, heavy metals are continuously being released by industrial activities and therefore, pollution monitoring is needed. Biomonitoring studies using macroalgae has given highly different assessments due to the variability in algal species and sampling time points. We carried out a systematic monthly sampling of brown algae (Phaeophyta) from three locations on the western coast of the Arabian Gulf between September and February 2018. One urban area (Uqair) and two oil refining areas (Ras Tanura and Jubail) were monitored due to they have a common brown macroalgae species composition. The incidence of Cystoseira myrica, C. trinodis C. osmundacea, Hormophysa cuneiformis, Sargassum aquifolium, S. latifolium, S. filipendula and Padina boryana varied among the sites and with the time of year within the sites. The concentrations of Co, Cd and Pb varied among the sampling sites, the algal species and the sampling time points remarkably. A tentative time-trend increasing towards February was observed for some species. However, it appeared that neither optimum sampling time point, nor superior brown algae species could be recommended. The highest heavy metal accumulation was observed in Padina boryana. However, this species grew only on the two oil polluted sites. We concluded that some brown algae species can be used for biomonitoring heavy metal pollution on the western coast of the Arabian Gulf. The species incidence should be monitored systematically and the species used should be chosen locally and sampled at the same time of the year.

Lead removal by Spirulina platensis biomass.

In this investigation, we report on the biosorption of Pb (II) from aqueous solutions by the nonliving biomass of the micro-alga (cyanobacterium) Spirulina platensis. Propagation of the micro-alga was carried out in outside oblong raceway ponds. The biomass was cleaned, dried and used for the investigation. The effects of pH, adsorbent dose, temperature, initial concentration of Pb (II), and contact time on the adsorption of lead by the dry biomass were studied. The experiments were carried out in 250 ml conical flasks containing 100 ml of test solutions using an orbital incubator at 150 rpm. Concentrations of the metal before and after the experiments were measured using Atomic Absorption Spectrophotometer. Very high levels of Pb (II) removal (>91%) were obtained. The optimum conditions for maximal adsorption by S. platensis were found to be pH 3; 2 g of adsorbent dose; incubation at 26°C; 100 mg/l of lead initial concentration and 60 minutes of contact time. The experimental data fitted well with Freundlich isotherm equation with R(2) values greater than 0.97. Based on our results, we recommend the utilization of S. platensis biomass for heavy metal removal from aqueous solutions.