Potential value of phosphate compounds in enhancing immobilization and reducing bioavailability of mixed heavy metal contaminants in shooting range soil

Shooting range soils contain mixed heavy metal contaminants including lead (Pb), cadmium (Cd), and zinc (Zn). Phosphate (P) compounds have been used to immobilize these metals, particularly Pb, thereby reducing their bioavailability. However, research on immobilization of Pb's co-contaminants showed the relative importance of soluble and insoluble P compounds, which is critical in evaluating the overall success of in situ stabilization practice in the sustainable remediation of mixed heavy metal contaminated soils. Soluble synthetic P fertilizer (diammonium phosphate; DAP) and reactive (Sechura; SPR) and unreactive (Christmas Island; CPR) natural phosphate rocks (PR) were tested for Cd, Pb and Zn immobilization and later their mobility and bioavailability in a shooting range soil. The addition of P compounds resulted in the immobilization of Cd, Pb and Zn by 1.56-76.2%, 3.21-83.56%, and 2.31-74.6%, respectively. The reactive SPR significantly reduced Cd, Pb and Zn leaching while soluble DAP increased their leachate concentrations. The SPR reduced the bioaccumulation of Cd, Pb and Zn in earthworms by 7.13-23.4% and 14.3-54.6% in comparison with earthworms in the DAP and control treatment, respectively. Bioaccessible Cd, Pb and Zn concentrations as determined using a simplified bioaccessibility extraction test showed higher long-term stability of P-immobilized Pb and Zn than Cd. The differential effect of P-induced immobilization between P compounds and metals is due to the variation in the solubility characteristics of P compounds and nature of metal phosphate compounds formed. Therefore, Pb and Zn immobilization by P compounds is an effective long-term remediation strategy for mixed heavy metal contaminated soils.

Comparative analysis of speciation and bioaccessibility of arsenic in rice grains and complementary medicines

In many countries, rice grains and complementary medicines are important sources of arsenic (As) consumption. The objective of this study was to compare the speciation and bioaccessibility of As in selected rice grains and complementary medicines. A number of rice grain samples, and a range of herbal and ayurvedic medicines were analyzed for total As, speciation of As using sequential fractionation and extended x-ray absorption fine structure (EXAFS) techniques, and bioaccessibility of As using an in vitro extraction test. The daily intake of As through the uptake of these As sources was compared with the safety guidelines for As. The results demonstrated higher levels of As in ayurvedic medicines compared to herbal medicines and rice grains. The sequential fractionation showed the dominance of organic-bound As species in rice grains and herbal medicines, however, inorganic-bound As species dominated the ayurvedic medicines. This implies that As is derived from plant uptake in herbal medicines and rice grains, and from inorganic mineral input in ayurvedic medicines. Arsenic bioaccessibility was higher in ayurvedic than herbal medicines and rice grains, suggesting that inorganic As added as a mineral therapeutic input is more bioaccessible than organic As species derived from plant uptake. This study also showed a positive relationship between soluble As fractions and bioaccessibility indicating that solubility is an important factor controlling bioaccessibility. The daily intake values for As as estimated by total As content are likely to exceed the safe threshold level in rice grains that are enriched with As.

Speciation and bioavailability of lead in complementary medicines

Complementary medicines have associated risks which include toxic heavy metal(loid) and pesticide contamination. The objective of this study was to examine the speciation and bioavailability of lead (Pb) in selected complementary medicines. Six herbal and six ayurvedic medicines were analysed for: (i) total heavy metal(loid) contents including arsenic (As), cadmium (Cd), Pb and mercury (Hg); (ii) speciation of Pb using sequential fractionation and extended x-ray absorption fine structure (EXAFS) techniques; and (iii) bioavailability of Pb using a physiologically-based in vitro extraction test (PBET). The daily intake of Pb through the uptake of these medicines was compared with the safety guidelines for Pb. The results indicated that generally ayurvedic medicines contained higher levels of heavy metal(loid)s than herbal medicines with the amount of Pb much higher than the other metal(loid)s. Sequential fractionation indicated that while organic-bound Pb species dominated the herbal medicines, inorganic-bound Pb species dominated the ayurvedic medicines. EXAFS data indicated the presence of various Pb species in ayurvedic medicines. This implies that Pb is derived from plant uptake and inorganic mineral input in herbal and ayurvedic medicines, respectively. Bioavailability of Pb was higher in ayurvedic than herbal medicines, indicating that Pb added as a mineral therapeutic input is more bioavailable than that derived from plant uptake. There was a positive relationship between soluble Pb fraction and bioavailability indicating that solubility is an important factor controlling bioavailability. The daily intake values for Pb as estimated by total and bioavailable metal(loid) contents are likely to exceed the safe threshold level in certain ayurvedic medicines. This research demonstrated that Pb toxicity is likely to result from the regular intake of these medicines which requires further investigation.

Landfills as a biorefinery to produce biomass and capture biogas

While landfilling provides a simple and economic means of waste disposal, it causes environmental impacts including leachate generation and greenhouse gas (GHG) emissions. With the introduction of gas recovery systems, landfills provide a potential source of methane (CH4) as a fuel source. Increasingly revegetation is practiced on traditionally managed landfill sites to mitigate environmental degradation, which also provides a source of biomass for energy production. Combustion of landfill gas for energy production contributes to GHG emission reduction mainly by preventing the release of CH4 into the atmosphere. Biomass from landfill sites can be converted to bioenergy through various processes including pyrolysis, liquefaction and gasification. This review provides a comprehensive overview on the role of landfills as a biorefinery site by focusing on the potential volumes of CH4 and biomass produced from landfills, the various methods of biomass energy conversion, and the opportunities and limitations of energy capture from landfills.

A comparison of the gum pads of Afro-Caribbean and Caucasian British subjects at birth

The gum pads of 34 subjects of Afro-Caribbean origin are compared with those of an equal number of Caucasian British subjects, matched for sex and birth weight. Some differences of size, form, and relationship are described, and are considered large enough to merit further investigation on a larger sample.