Environmental Pollution Series B, Chemical and Physical最新文献

Uptake of Hg(II) (1–10 mg litre⁻¹) by two humic acids varied with pH, with >98% being sorbed at pH 4–5. Langmuir plots yielded adsorption capacity and bonding values of ∼50 mmol kg⁻¹ and 3 × 10⁶ litre mol⁻¹ respectively. The addition of increasing amounts of chloride reduced uptake (10–20%) and shifted the maximum sorption region to higher pH values. The presence of 10⁻² M levels of Ca²⁺, Mg²⁺ and NH₄⁺ promoted near total adsorption and reduced the pH effect; 10⁻⁴ levels slightly increased the amount of Hg(II) sorbed. Sulphate additions reduced Hg uptake. Much of the Hg(II) is considered to be chemisorbed, since while most of the sorbed species was extractable in 0·005 m EDTA, only half was released into 1 m HNO₃ and molar salt solutions retrieved less than a third.

The environmental significance of the results are discussed.

The amounts of Mn, Cr, Pb, Zn, Cu and Ni in the lichens Squamarina crassa, Teloschistes lacunosus, Ramalina maciformis, Diploschistes steppicus and Caloplaca ehrenbergii growing in the Negev Desert, Israel, were measured. The amount of Pb in S. crassa growing close to a main motorway was relatively high and much higher than in the soil—the substrate of S. crassa. The high coefficients of variation for Mn and Cu found in several lichens are attributed to large particles entrapped in the lichen thallus. It is suggested that the low coefficients of variation found for Zn in all the lichens studied indicate that this element occurs in small, well-dispersed particles.

Measuring the heavy metal content of desert lichens is important because of their biomonitoring potential and also because snails and goats feed on them.

Aquatic bryophyes have been analysed for aluminium, manganese and zinc to assess the feasibility of using these plants as bioindicators of metal loadings to acid streams and lochs in two regions of Scotland. Bioconcentration occurred in all waters but increased hydrogen ion concentrations in the water were associated with decreased metal concentrations in the bryophytes. Release of aluminium, manganese and zinc from the bryophytes by hydrogen ions may make a significant contribution to the loadings of these metals in acid waters.

The mobility patterns of four divalent heavy metals—Zn²⁺, Cu²⁺, Pb²⁺ and Cd²⁺—were determined under varying acidities in an artificially contaminated sand and a naturally polluted soil after the addition of various organic materials—farm yard manure (FYM), peat, humic acid (HA) and tetraethylene pentamine (Tetren). Due to dissolution and decomplexation, the mobility of the heavy metals increased considerably upon progressive acidification. Metal pairs ZnCd and CuPb showed almost similar mobility patterns. In the case of artificially contaminated scand, the addition of FYM and peat enhance the mobility of heavy metals at lower pH values and decreased it at higher pHs. Humic acid and Tetren had little effect.

Copper, nickel and iron levels were higher in samples of substrate, leachate and surface water of copper-nickel mine tailings than in those from uranium mine wastes or a control area, which were similar. Nickel and iron were also elevated in the vegetation from the copper-nickel workings. The gut of resident voles was contaminated by copper and nickel and the skin and hair by nickel and iron. Higher whole body burdens of copper and nickel were attributed to the higher levels in gut and skin. Higher levels of iron observed in bone and kidney tissue were the only indications of internal deposition of these metals. Cobalt, zinc and lead levels, when detectable, in leachate, vegetation and water differed little from, or were below, control levels in both tailings. Total body concentration of cobalt was lowest in animals from uranium mine tailings; their low skin contamination was due to low levels in the substrate. Total body burden of zinc did not differ among sites. No internal deposition of cobalt was seen. Although lead levels were higher in uranium mine tailings than elsewhere, no differences were seen in lead concentrations in vegetation or resident voles. Radium-226 was detected only in the samples and voles of uranium mine wastes; the voles carried the radium-226 in their gut, skin and skeleton.

Eight plant species—Acacia melanoxylon, Bauhinia malabarica, Bougainvillea glabra, Calotropis procera, Catharanthus roseus, Eucalyptus globulus, Ipomoea fistulosa and Peltophorum pterocarpum—were collected from a newly established suburb colony of Lucknow city, where the major pollutant is dust, to study cleansing efficiency of the plant canopy and also to establish the correlation between the leaf morphological characteristics and their dust trapping potential. The dust load, in milligrams per square centimetre of leaf surface, was measured and related to foliar epidermal and cuticular characteristics, and morphological features.

The rate and extent of the methylation of inorganic mercury has been shown to depend markedly on the chemical speciation of the mercury and the methylating agent. The presence of mercury (II)—chlorine covalent bonding has an inhibitory effect on methylation by methyl cobalamin (CH₃CoB₁₂) and in natural sediments. The rôle of radical and carbonium ion methylation mechanisms has also been investigated. In a typical estuarine sediment the extent of mercury methylation is as follows: Hg(OAc)₂ ⪢ Hg(cyst)₂ > Hg(cyst) (Hcyst)Cl > Hg(meth)₂²⁺ > Hg(eth)₂²⁺ > Hg(Hcyst)Cl₂ > HgCl₂ > (HgCl₂)₂ pen, where OAc = acetateHcyst = cysteine, meth = methionine, eth = ethionine and pen = penicillamine. This is consistent with mercury methylation arising by attack of a methyl carbanion (CH₃⁻) on inorganic mercury (II) ions derived by microbial breakdown of the original and mercury compounds added.

Arsenic levels have been determined in the hair and nails of male employees of a wood preservative treatment factory in Nigeria. Mean As concentrations of 11·6, 7·5, 4·1 and 1·6 μg g⁻¹ were measured in hair samples from four groups of employees, depending on the nature of their work and the duration of their employment in the factory. Mean As levels of 7·4, 4·8, 2·7 and 1·0 μg g⁻¹ were also measured in nails for the same groups. The employees involved in the preparation of the treating fluids, the chemical impregnation process and handling of the treated timber showed consistently higher As levels in both tissues than those who were less exposed to the chemicals. No correlation between the measured As levels and age of the donors was established, nor was a reasonably good hair As—nail As correlation obtained for any of the four exposure groups. This study, however, minimized possible effects of age, sex, hair colour and chemical treatment. Mean As levels of 1·2 and 0·64 μg g⁻¹ as ‘control’ values were also determined in hair and nails, respectively of ‘non-exposed’ persons in the same age group as the factory workers. The elevated As levels measured in both tissues reflected a relatively high degree of exposure to the chemicals.