Transformation of zinc oxide nanoparticles in the presence of aluminum oxide with pre-sorbed phosphorus ligands.

Naturally occurring oxides could react with zinc oxide (ZnO) nanoparticles (NPs) and then change its transformation and toxicity to ecological receptors. The reaction may be affected by a variety of environmental factors, yet the relevant processes and mechanisms are limitedly investigated. Natural prevalent ligands, as an important factor, can sorb on natural oxide minerals and change its surface property, finally affecting ZnO NP transformation. This study investigated the interactions of ZnO NPs with phosphorus ligands (i.e., phytate and orthophosphate) pre-sorbed γ-alumina (γ-Al2O3) via batch experiments and multi-technique analyses. A limited amount of aqueous Zn2+ is observed when the concentration of ZnO NPs is relatively low (<64.8 mg L-1) in the presence of phytate pre-sorbed γ-Al2O3. Solid Zn(II) species includes binary/ternary surface Zn(II) complexes on γ-Al2O3 with minor amounts of zinc phytate precipitates. As the concentration of ZnO NPs increases, surface Zn(II) complexes gradually transform into zinc phytate and Zn-Al layered double hydroxide (Zn-Al LDH) precipitates. The quantitative analysis indicates that, as the concentration of ZnO NPs increases from 32.4 to 388.8 mg L-1, the proportion of Zn(II) species as binary/ternary surface complexes decreases from 81.9 to 30.2%; and the proportion as zinc phytate and Zn-Al LDH increases from 17.9 to 27.6% and 0 to 43.8%, respectively. The pre-sorption of orthophosphate can also inhibit ZnO NP transformation into Zn-Al LDH precipitates on γ-Al2O3. This study suggests that natural ligands pre-existed on natural oxide minerals could greatly influence the solubility, stability, transformation, and fate of easily dissoluble metal oxides (e.g., ZnO) in the environments.

Coevolution of Iron, Phosphorus, and Sulfur Speciation during Anaerobic Digestion with Hydrothermal Pretreatment of Sewage Sludge.

Anaerobic digestion (AD) with hydrothermal (HT) pretreatment is an emerging technology for enhanced resource recovery from sewage sludge. This study investigates the speciation of Fe, P, and S during sequential HT-AD treatment of sewage sludge using sequential chemical extraction, X-ray diffraction, and X-ray absorption spectroscopy. Results suggest strong correlations between Fe and P species as well as Fe and S species, affecting the solubility and bioavailability of each other. For instance, much vivianite formed in the hydrochars after HT treatment at low temperature, while more strengite precipitated at higher HT temperature. During the subsequent AD process, microbial reduction of strengite and other Fe(III) species led to the formation of more vivianite, with concurrent P release into the solution and adsorption onto other minerals. HT pretreatment of sewage sludge had a weak effect on the sulfidation of Fe during the AD process. This work has important implications for understanding the nutrient speciation and availability in sludge-derived hydrochars and AD solids. It also provides fundamental knowledge for the selection and optimization of HT pretreatment conditions for enhanced resource recovery through sequential HT-AD process.

Polyphosphate Adsorption and Hydrolysis on Aluminum Oxides.

The geochemical behaviors of phosphate-containing species at mineral-water interfaces are of fundamental importance for controlling phosphorus mobility, fate, and bioavailability. This study investigates the sorption and hydrolysis of polyphosphate (a group of important long-chained phosphate molecules) on aluminum oxides in the presence of divalent metal cations (Ca2+, Cu2+, Mg2+, Mn2+, and Zn2+) at pH 6-8. γ-Al2O3 with three particle sizes (5, 35, and 70 nm) was used as an analogue of natural aluminum oxides to investigate the particle size effect. All metal cations enhanced polyphosphate hydrolysis at different levels, with Ca2+ showing the most significant enhancement, and the difference in the enhancement might be due to the intrinsic affinity of metal cations to polyphosphate. In the presence of Ca2+, the hydrolysis rate decreased with increasing mineral particle size. Solid-state 31P nuclear magnetic resonance spectroscopy (NMR) revealed the main surface P species to be amorphous calcium phosphate precipitates, phosphate groups in polyphosphate that formed direct bonds with the mineral surface as inner-sphere complexes, and phosphate groups in polyphosphate that were not directly bonded to the mineral surfaces. Our results reveal the critical roles of mineral-water interface processes and divalent metal cations on controlling polyphosphate speciation and transformation and phosphorus cycling.

Formation of Zn-Al layered double hydroxides (LDH) during the interaction of ZnO nanoparticles (NPs) with γ-Al2O3.

Zinc and aluminum layered double hydroxides (Zn-Al LDH) are a common group of major Zn species in various Zn-contaminated soil/sediment environments, yet their formation pathways and underlying mechanisms under varied conditions are not well understood. This study investigated the formation of Zn-Al LDHs through the direct interaction of two solid substrates, ZnO nanoparticles (NPs) and a representative Al oxide, γ-Al2O3. Batch experiments and complementary microscopic and spectroscopic analyses were conducted to elucidate the reaction kinetics and mechanisms, as well as the morphologic and structural evolution of the products. Dissolved Zn and Al concentrations decreased significantly in a dual solid system compared to a single solid system. A bulk Zn-Al LDH phase was found to form under a wide pH range (6.5-9.5). Aside from Zn-Al LDH, γ-Al2O3 was the main remaining solid phase at pH 6.5, whereas ZnO NPs were the main residual solid phases at pH 9.5. Formation of amorphous Zn(OH)2 was also observed at both pH values, likely due to Zn2+ release at low pH and Al(OH)4- adsorption at high pH. It is proposed that the formation of Zn-Al LDH occurs via a dissolution-sorption-coprecipitation process, where the solubility of ZnO NPs or γ-Al2O3 solid phases determines the reaction pathways and kinetics under varied pH conditions. The results from this work revealed the transformation mechanisms for ZnO NPs under conditions from weakly acidic to alkaline pH with highly available Al particles and shed light on the environmental fate of ZnO NPs in Zn or ZnO NP contaminated environments.

Phosphatase-Mediated Hydrolysis of Linear Polyphosphates.

Polyphosphates are a group of phosphorus (P) containing molecules that are produced by a wide range of microorganisms and human activities. Although polyphosphates are ubiquitous in aquatic environments and are of environmental significance, little is known about their transformation and cycling. This study characterized the polyphopshate-hydrolysis mechanisms of several representative phosphatase enzymes and evaluated the effects of polyphosphate chain length, light condition, and calcium (Ca2+). 31P nuclear magnetic resonance (NMR) spectroscopy was used to monitor the dynamic changes of P molecular configuration during polyphosphate hydrolysis and suggested a terminal-only degradation pathway by the enzymes. Such mechanism enabled the quantification of the hydrolysis rates by measuring orthophosphate production over time. At the same initial concentration of polyphosphate molecules, the hydrolysis rates were independent of chain length. The hydrolysis of polyphosphate was also unaffected by light condition, but was reduced by the presence of Ca2+. The released orthophosphates formed Ca-phosphate precipitates in the presence of Ca2+, likely in amorphous phases. Results from this study lay the foundation for better understanding the chemical processes governing polyphosphate transport and transformation in various environmental settings.

[Advances in the pathway and molecular mechanism for the biodegradation of microcystins].

With increasing discharge of wastewater containing nitrogen and phosphorus into rivers and lakes, harmful cyanobacterial blooms have become more frequent worldwide. The main harm of cyanobacterial blooms is producing and releasing a great amount of algal toxins mainly containing microcystins (MCs). Since MCs are extremely harmful to plants and animals and difficult to be removed efficiently by the traditional processing methods, how to control harmful cyanobacterial blooms and remove MCs have become an unsolved problem in the field of environmental science all over the world. This paper summarized the structure and toxicity of MCs, the MCs-biodegrading bacterial strains, the enzymes, the genes, and the biodegradation pathway and molecular mechanism of MCs. The further research subjects were also proposed. It was hoped that this review could provide a reference for restoring MCs-polluted lakes and reservoirs and ensuring drinking water safety.

[Effects of scalp acupuncture on expression of hippocampal MMP-9 in cerebral ischemia injury rats].

OBJECTIVE: To observe the effect of scalp-acupuncture on the expression of matrix metalloproteinase 9 (MMP-9) in the endothelium of the microvessels in the hippocampal CA 3 area in local cerebral ischemia (CI) rats, so as to study its underlying mechanism in improving CI. METHODS: Eighty male Wistar rats were randomized into normal control (n = 8), sham-operation (n = 8), CI model (n = 32), and scalp-acupuncture (n = 32) groups. The later two groups were further equally and respectively divided into 1, 3, 5 and 10 d subgroups. CI model was established by occlusion of the middle cerebral artery (MCAO). "Baihui" (GV 20) and "Qubin"(GB 7) were punctured with filiform needles and stimulated by twirling the needle at a frequency of about 200 revolutions/min for 1 min. The needles were retained for 30 min and re-manipulated once again every 10 min. The treatment was given once daily, continuously for 1, 3, 5 and 10 days respectively in different subgroups. MMP-9 immunoactivity of hippocampal CA 3 area was assayed by immunohistochemistry (SABC). RESULTS: Following CI, the CI rats' neural deficit scores in the model and scalp-acupuncture (treatment) groups had no apparent difference (P > 0.05). After acupuncture, the neural deficit score in the treatment group decreased gradually, and was significantly lower than that in the 10 d subgroup of model group (P < 0.05). Compared with the 1, 3, 5 and 10 d subgroups of control group, the total area and integral optical density (IOD) values of MMP-9 immunoactivity of hippocampal CA 3 area were all increased significantly in the corresponding 4 subgroups of model group (P < 0.01). Compared with the 3, 5 and 10 d subgroups of the model group, the total area and IOD values of MMP-9 immunoreaction positive products in the corresponding 3 subgroups of scalp-acupuncture group were decreased significantly (P < 0.05, P < 0.01). CONCLUSION: Scalp-acupuncture can effectively down-regulate MMP-9 expression in the hippocampal CA 3 area in focal cerebral ischemia rats, which may contribute to its effect in improving the neural deficit.

Therapeutic effect of dietary boron supplement on retinoic acid-induced osteoporosis in rats / 南方医科大学学报

<p><b>OBJECTIVE</b>To observe the therapeutic efficacy of dietary boron supplement on retinoic acid-induced osteoporosis in rats, so as to provide experimental evidence for clinical management of osteoporosis with boron.</p><p><b>METHODS</b>Thirty-two SD rats were randomized into normal control group (8 rats) and osteoporotic group (24 rats), and osteoporosis was induced in rats of the latter group by intragastric retinoic acid administration at the daily dose of 80 mg/kg for 15 consecutive days. The osteoporotic rats were subdivided into control group (8 rats) without treatment, boron treatment group (8 rats) and estradiol treatment group (8 rats). After 30 days of treatment, the serum contents of Ca, P, boron and the activities of alkaline phosphatase (AKP) and tartrate-resistant acid phosphatase (TRAP) in the rats were assayed, the bone mineral density (BMD) of the whole body, lumbar vertebrae and tibia were determined, and the morphological changes of the femurs were observed.</p><p><b>RESULTS</b>The serum contents of Ca and P in the rats of the 4 groups differed scarcely, but the content of boron in boron treatment group was markedly higher than that in the other three groups. In the osteoporotic control group, the activities of serum AKP and TRAP, the masses of spongy bone and cortical bone of the femurs, and the quantity of the osteoclasts were increased, with the BMD of the lumbar vertebrae and tibia decreased, suggesting osteoporotic conditions. The mean trabecular plate density and thickness, trabecular bone volume and cortical bone volume of the femurs in the osteoporotic rats treated with boron or estradiol were significantly increased, but the active osteoclast quantity in the spongy bone and serum TRAP activities were obviously decreased, and the bone quality was comparable with that of the normal group. In addition, the serum AKP activity and the active osteoblast quantity in the spongy bone were obviously increased in boron treatment group.</p><p><b>CONCLUSION</b>The dietary boron supplement can increase the serum content of boron of osteoporotic rats to stimulate bone formation and inhibit bone resorption, producing therefore obvious therapeutical effect against osteoporosis.</p>

[Therapeutic effect of dietary boron supplement on retinoic acid-induced osteoporosis in rats].

OBJECTIVE: To observe the therapeutic efficacy of dietary boron supplement on retinoic acid-induced osteoporosis in rats, so as to provide experimental evidence for clinical management of osteoporosis with boron. METHODS: Thirty-two SD rats were randomized into normal control group (8 rats) and osteoporotic group (24 rats), and osteoporosis was induced in rats of the latter group by intragastric retinoic acid administration at the daily dose of 80 mg/kg for 15 consecutive days. The osteoporotic rats were subdivided into control group (8 rats) without treatment, boron treatment group (8 rats) and estradiol treatment group (8 rats). After 30 days of treatment, the serum contents of Ca, P, boron and the activities of alkaline phosphatase (AKP) and tartrate-resistant acid phosphatase (TRAP) in the rats were assayed, the bone mineral density (BMD) of the whole body, lumbar vertebrae and tibia were determined, and the morphological changes of the femurs were observed. RESULTS: The serum contents of Ca and P in the rats of the 4 groups differed scarcely, but the content of boron in boron treatment group was markedly higher than that in the other three groups. In the osteoporotic control group, the activities of serum AKP and TRAP, the masses of spongy bone and cortical bone of the femurs, and the quantity of the osteoclasts were increased, with the BMD of the lumbar vertebrae and tibia decreased, suggesting osteoporotic conditions. The mean trabecular plate density and thickness, trabecular bone volume and cortical bone volume of the femurs in the osteoporotic rats treated with boron or estradiol were significantly increased, but the active osteoclast quantity in the spongy bone and serum TRAP activities were obviously decreased, and the bone quality was comparable with that of the normal group. In addition, the serum AKP activity and the active osteoblast quantity in the spongy bone were obviously increased in boron treatment group. CONCLUSION: The dietary boron supplement can increase the serum content of boron of osteoporotic rats to stimulate bone formation and inhibit bone resorption, producing therefore obvious therapeutical effect against osteoporosis.