The purpose of this paper was to use quantitative systems-level approach employing biotic ligand model based threshold damage model to examine physiological responses of tilapia and freshwater clam to sequential pulsed and fluctuating arsenic concentrations. We tested present model and triggering mechanisms by carrying out a series of modeling experiments where we used periodic pulses and sine-wave as featured exposures. Our results indicate that changes in the dominant frequencies and pulse timing can shift the safe rate distributions for tilapia, but not for that of freshwater clam. We found that tilapia increase bioenergetic costs to maintain the acclimation during pulsed and sine-wave exposures. Our ability to predict the consequences of physiological variation under time-varying exposure patterns has also implications for optimizing species growing, cultivation strategies, and risk assessment in realistic situations.

Batch adsorption experiments were carried out to study the adsorptive removal and diffusion mechanism of para-chlorophenol (p-CP) onto Calgon Filtrasorb 400 (F400) activated carbon. The external mass transfer resistance is negligible in the adsorption process carried out under different conditions in batch operation. Intraparticle diffusion model plots were used to correlate the batch p-CP adsorption data; three distinct linear sections were obtained for every batch operation. The textural properties of F400 activated carbon showed that it has a large portion of supermicropores, which is comparable to the size of the p-CP molecules. Due to the stronger interactions between p-CP molecules and F400 micropores, p-CP molecules predominantly diffused and occupied active sites in micropore region by hopping mechanism, and eventually followed by a slow filling of mesopores and micropores. This hypothesis is proven by the excellent agreement of the intraparticle diffusion model plots and the textural properties of F400 activated carbon.

In streams, periphyton biofilms are important sinks for trace metals such as cadmium and are primary food sources of many invertebrate consumers. To study Cd trophic transfer, we produced differentially contaminated diets by exposing natural periphyton to environmentally relevant dissolved Cd ranging from 0 to 10 μg L−1 for 6–7 days using a radiotracer approach. On average, periphyton grown during three different seasons bioconcentrated Cd similarly – approximately 1315 (±442) -fold above dissolved concentrations. However, mayfly larvae (Centroptilum triangulifer) raised on these differentially contaminated diets (first instar through adulthood) had significantly higher trophic transfer factors from periphyton grown in Aug and Nov 2008 (4.30 ± 1.55) than from periphyton grown in Jan 2009 (0.85 ± 0.21). This Cd bioaccumulation difference is only partially explained by apparent food quality and subsequent growth differences. Taken together, these results suggest that primary producers at the base of food webs drive metal bioaccumulation by invertebrate grazers. Periphyton is a major source of Cd bioaccumulation in a grazing mayfly.

The transformation of DDT was studied in an anaerobic system of dissimilatory iron-reducing bacteria (Shewanella decolorationis S12) and iron oxide (α-FeOOH). The results showed that S. decolorationis could reduce DDT into DDD, and DDT transformation rate was accelerated by the presence of α-FeOOH. DDD was observed as the primary transformation product, which was demonstrated to be transformed in the abiotic system of Fe2+ + α-FeOOH and the system of DIRB + α-FeOOH. The intermediates of DDMS and DBP were detected after 9 months, likely suggesting that reductive dechlorination was the main dechlorination pathway of DDT in the iron-reducing system. The enhanced reductive dechlorination of DDT was mainly due to biogenic Fe(II) sorbed on the surface of α-FeOOH, which can serve as a mediator for the transformation of DDT. This study demonstrated the important role of DIRB and iron oxide on DDT and DDD transformation under anaerobic iron-reducing environments.

To investigate the effects of ambient-level gas-phase peroxides concurrent with O3 on foliar injury, photosynthesis, and biomass in herbaceous plants, we exposed Japanese radish (Raphanus sativus) to clean air, 50 ppb O3, 100 ppb O3, and 2-3 ppb peroxides + 50 ppb O3 in outdoor chambers. Compared with exposure to 100 ppb O3, exposure to 2-3 ppb peroxides + 50 ppb O3 induced greater damage in foliar injury, net photosynthetic rates and biomass; the pattern of foliar injury and the cause of net photosynthetic rate reduction also differed from those occurring with O3 exposure alone. These results indicate for the first time that sub-ppb peroxides + 50 ppb O3 can cause more severe damage to plants than 100 ppb O3, and that not only O3, but also peroxides, could be contributing to the herbaceous plant damage and forest decline observed in Japan's air-polluted urban and remote mountains areas.

Two peat bogs from remote alpine sites in Australia were found to contain detailed and coherent histories of atmospheric metal pollution for Pb, Zn, Cu, Mo, Ag, As, Cd, Sb, Zn, In, Cr, Ni, Tl and V. Dramatic increases in metal deposition in the post-1850 AD portion of the cores coincide with the onset of mining in Australia. Using both Pb isotopes and metals, pollutants were ascribed to the main atmospheric pollution emitting sources in Australia, namely mining and smelting, coal combustion and agriculture. Results imply mining and metal production are the major source of atmospheric metal pollution, although coal combustion may account for up to 30% of metal pollutants. A novel finding of this study is the increase in the otherwise near-constant Y/Ho ratio after 1900 AD. We link this change to widespread and increased application of marine phosphate fertiliser in Australia's main agricultural area (the Murray Darling Basin).

The effect of elevated CO2 and O3 on apparent quantum yield (), maximum photosynthesis (Pmax), carboxylation efficiency (Vcmax) and electron transport capacity (Jmax) at different canopy locations was studied in two aspen (Populus tremuloides) clones of contrasting O3 tolerance. Local light climate at every leaf was characterized as fraction of above-canopy photosynthetic photon flux density (ÆPPFD). Elevated CO2 alone did not affect or Pmax, and increased Jmax in the O3-sensitive, but not in the O3-tolerant clone. Elevated O3 decreased leaf chlorophyll content and all photosynthetic parameters, particularly in the lower canopy, and the negative impact of O3 increased through time. Significant interaction effect, whereby the negative impact of elevated O3 was exaggerated by elevated CO2 was seen in Chl, N and Jmax, and occurred in both O3-tolerant and O3-sensitive clones. The clonal differences in the level of CO2 × O3 interaction suggest a relationship between photosynthetic acclimation and background O3 concentration. Photosynthetic acclimation to elevated CO2 depends on the background oxidant levels.

The accumulation and rhizotoxicity of Ni to pea were investigated. Calcium, H, and Ni competed for root-binding sites with high pH and low Ca favoring more Ni accumulation. At low pH, Ca accumulation is the key factor determining root growth, while at medium to high pH, root elongation is more sensitive to Ni concentration. The tissue concentration of Ni and Ca ([Ni]t or [Ca]t, μmol g-1 dry root) can be predicted from total dissolved Ni ([Ni]T, μM), pH, and total dissolved Ca ([Ca]T, mM) by two approaches. Approach 1 is the empirical equations [Ni]t = (0.361 pH-0.695[Ca]T)*[Ni]T and [Ca]t = 8.29 pH + 10.8 [Ca]T. The second approach involves a two-step model. The surface-bound Ni and Ca are estimated from a surface adsorption model with binding constants derived from independent ion adsorption experiments. Then transfer functions are used to predict internal root Ni and Ca accumulation.

To clarify the effects of O3 on crop plants cultivated in Bangladesh, two Bangladeshi wheat cultivars (Sufi and Bijoy) were grown in plastic boxes filled with Andisol and exposed daily to charcoal-filtered air or O3 at 60 and 100 nl l-1 (10:00-17:00) from 13 March to 4 June 2008. The whole-plant dry mass and grain yield per plant of the two cultivars at the final harvest were significantly reduced by the exposure to O3. Although there was no significant effect of O3 on stomatal diffusive conductance to H2O of flag leaf, net photosynthetic rate of the leaf was significantly reduced by the exposure to O3. The sensitivity of growth, yield, yield components and leaf gas exchange rates to O3 was not significantly different between the two cultivars. The results obtained in the present study suggest that ambient levels of O3 may detrimentally affect wheat production in Bangladesh.

The consumption of paddy rice (Oryza sativa L.) is a major inorganic arsenic exposure pathway in S.E. Asia. A multi-location survey was undertaken in Guangdong Province, South China to assess arsenic accumulation and speciation in 2 rice cultivars, one an Indica and the other a hybrid Indica. The results showed that arsenic concentrations in rice tissue increased in the order grain < husk < straw < root. Rice grain arsenic content of 2 rice cultivars was significant different and correlated with phosphorus concentration and molar ratio of P/As in shoot, being higher for the Indica cultivar than for the hybrid Indica, which suggests altering shoot phosphorus status as a promising route for breeding rice cultivars with reduced grain arsenic. Speciation of grain arsenic, performed using HPLC-ICP-MS, identified inorganic arsenic as the dominant arsenic species present in the rice grain.