Contamination Assessment of Mangrove Ecosystems in the Red Sea Coast by Polycyclic Aromatic Hydrocarbons.

Mangroves are known as a naturally based solution for climate mitigation and adaptation. Mangroves are at a potential risk of degradation by contaminants such as polycyclic aromatic hydrocarbons (PAHs). In this study, sixteen priority PAHs were analyzed and characterized in forty samples of mangrove seawater and mangrove sediments collected from two coastal areas (i.e., Sharm and Khor Rabigh) along the Red Sea Coast of Rabigh city in August 2013. We found that the average concentration of total PAH in mangrove sediments in the Sharam area (22.09 ng/kg) was higher than that in the Alkhor area (6.51 ng/kg). However, the average concentration of the total PAH in the mangrove seawater in the Alkhor area (9.19 ng/L) was double that in the Sharam area (4.33 ng/L). Phenanthrene and pyrene were the major components in both the mangrove seawater and sediment in all the investigated areas. We observed that the abundance of PAHs with 2-3 aromatic rings was dominant in sediment samples collected from both study areas. This abundance was also observed in seawater from the Sharam area. However, seawater samples from the Alkhor area had abundant PAHs with four aromatic rings. The majority of PAHs in sediment samples of both study areas originated from petrogenic sources, whereas the majority of PAHs in seawater samples originated from pyrogenic sources.

Firefighter exposures to organic and inorganic gas emissions in emergency residential and industrial fires.

The gas emissions generated from fires could cause mortalities and diseases in firefighters. Gas emissions from fire contain a mixture of a wide range of organic and inorganic gases, depending on several elements that are not currently known. In this study, firefighters were equipped with portable gas detectors to measure selected organic and inorganic gases in 26 emergency fire incidents. The fire incidents were categorized as industrial or residential based on their source. The exposure of firefighters to volatile organic compounds (VOCs) in residential fires was double that in industrial fires. This is probably due to the contents of the houses, as more VOCs are released from textiles and furniture. The concentration of toluene, which is widely used in cosmetics and paints in housing, was fifteen-fold higher in residential fires than industrial fires. The exposure of firefighters to inorganic gases was much higher in industrial fires than residential fires. The concentration of hydrogen chloride, which is generated from the combustion of chlorinated plastics, such as industrial pipes and cables, in industrial fires was 18-fold higher than that in residential fires. Additionally, in this study, we found that the concentration of VOCs that poses cancer and non-cancer health risk to firefighters increases in residential fire incidents to almost three times that in industrial fire incidents. Hydrogen sulfide and sulfur dioxide concentrations were higher in industrial fire incidents than in residential fire incidents. The level of hydrogen sulfide and sulfur dioxide were 19-fold and 8-fold higher, respectively, in industrial fire incidents than in residential fire incidents. This study reveals that gas emissions vary widely between industrial and residential fires.

Contamination and risk levels of metals associated with urban street dust in Riyadh, Saudi Arabia.

Urban street dust was collected from 22 locations in Riyadh, Saudi Arabia, and nine metals (Pb, Cr, Zn, Co, Cu, Al, Fe, Mn, and Ni) were investigated. The concentrations of these metals were employed in several common contamination evaluation indices to examine the contamination and the health risk caused by metals. Evaluation of these indices showed that they had variable degrees of contamination sensitivity. For individual contaminating elements (Pb, Cr, Zn, Co, Cu, and Ni), the sensitivities of the contamination of contamination factor (CF), the potential ecological risk (Ei), and geo-accumulation index (Igeo) were very similar. Therefore, these indices should yield very similar results. However, enrichment factor (EF) exhibited a different sensitivity pattern for determining the contamination caused by metals compared with the contamination level indicated by the other indices used in this study. Therefore, to avoid potential false indication of contamination, it is not recommended to use EF alone for determining contamination level. As indicated by four contamination evaluation indices (CF, Ei, Igeo, and EF), Riyadh was mainly contaminated by Pb. However, the health risk assessment results revealed that the Pb contamination level did not exceed the significant risk level for non-cancer effects. The cancer risk values indicated a negligible cancer risk to inhabitants of Riyadh exposed to metals associated with street dust. Considering the comprehensive contamination evaluation indices, the ecological risk index (RI) showed that about 77% of the sampling locations featured high ecological risk of which approximately 41% also featured high contamination indicated by pollution load index (PLI).

Influence of Different Urban Structures on Metal Contamination in Two Metropolitan Cities.

The influence of urban structures and land use patterns of metropolitan cities on the distribution of contaminants is not well understood. In this study, two metropolitan cities [Jeddah (a typical corridor city) and Madinah (a typical compact city)], featuring different spreading patterns and urban structures, were selected to investigate the contamination level and potential risk caused by metals (i.e., Pb, Zn, Co, Fe, Al, Cr, Cu, Ni, and Mn) associated with urban dust. The findings of this study show that a metropolitan city with a limited variety of activities and a polar center (e.g., Madinah) displays a typical distribution pattern of metals, i.e., concentrations of metals increase gradually toward the center of the city. In contrast, a metropolitan city with multiple major activities (e.g., Jeddah) displays a different distribution pattern, controlled by multiple key actors (e.g., seaports, oil refineries, and desalination/power plants) able to shift the location of highest contamination away from the city center. The above findings are supported by the results of several contamination and health indices. In Jeddah, the highest Pb contamination was found near an oil refinery based on geoaccumulation index (Igeo), contamination factor (CF), enrichment factor (EF), and ecological risk (Ei) values; whereas, the highest Zn contamination was found near a seaport, based on EF, CF, and Ei values. However, in Madinah, the contamination indices indicate that the most contaminated locations are near the city center. The highest non-carcinogenic health risk in Jeddah was found near an oil refinery and in the city center; whereas in Madinah, it was found mainly in the city center. Although there is no significant risk of cancer due to metals associated with dust in the two cities, Cr, representing a health risk contribution of >24%, was the major contributor of non-carcinogenic health risk in the two metropolitan cities.

Metal contamination decrease with new legislation: A decade of metal risk assessment in urban dust.

New scientific discoveries for new applications of materials (e.g., metals) lead to extensive industrial use of these materials, which in turn, has significant negative health and environmental impacts. Governments use legislation as a management tool to control the usage of certain materials to lower contamination. This study investigates the level of metal contamination over a period of 12 years to observe the dynamic changes in response to new legislation or industrial improvements. Metals (i.e., Pb, Zn, Co, Cu) associated with urban roadside dust in 21 sites in Riyadh, Saudi Arabia were analyzed during the period of 2001-2013. Three main conclusions were drawn from this study: 1) Phasing out leaded gasoline was an effective tool to control Pb contamination. The average Pb concentration in the city was 37 times higher in 2001 compared to that in 2013. Twenty-nine percent of the investigated sites were at a significant health risk in 2001 compared to none in 2013. 2) The new substitutes of Zn oxides and new limitations of the Zn content in the rubber industry were effective at controlling the Zn contamination in the urban environment. The average Zn concentration of the city was 8 times higher in 2001 compared to that in 2013. Eighty-one percent of the investigated sites in 2001 were considered to be very highly contaminated (CF > 6) compared to none in 2013. 3) The lack of legislation regarding the Co-content in fossil fuels was probably the main reason for the enhancement of the Co contamination in the whole city, with an increase in the average Co concentration >3 times in 2013 compared to that in 2001. Likewise, the health risk index was increased by ∼3 times from 2001 to 2013. For Cu, the average Cu concentration in 2001 was almost twice that in 2003 and 2013. Legislation has been observe to be an effective management tool for controlling metal contamination.

Competition by aquifer materials in a bimetallic nanoparticle/persulfate system for the treatment of trichloroethylene.

It has been suggested in the literature that aquifer materials can compete with the target organic compounds in an activated peroxygen system. In this study, we employed a rapid treatment method using persulfate activated with bimetallic nanoparticles to investigate the competition between aquifer materials and the dissolved phase of a target organic compound. The concentration of dissolved trichloroethylene (TCE) remaining after using the activated persulfate system was two- to three-fold higher in a soil slurry batch system than in an aqueous batch system. For all five aquifer materials investigated, an increase in the mass of the aquifer solids significantly decreased the degradation of TCE. A linear relationship was observed between the mass of aquifer materials and the initial TCE degradation rate, suggesting that the organic carbon and/or aquifer material constituents (e.g., carbonates and bicarbonates) compete with the oxidation of TCE.