Characteristics and emissions of isoprene and other non-methane hydrocarbons in the Northwest Pacific Ocean and responses to atmospheric aerosol deposition.

Field investigations in the Northwest Pacific Ocean were carried out to determine the distributions of marine and atmospheric non-methane hydrocarbons (NMHCs), sources and environmental effects. We also conducted deck incubation experiments to investigate the effects of atmospheric aerosol deposition on NMHCs production. The marine NMHCs displayed an increasing trend from the South Equatorial Current to the Oyashio Current. The enhanced phytoplankton biomass and dissolved organic materials (DOM) content in the Kuroshio-Oyashio Extension contributed significantly to isoprene and NMHCs production compared with those in tropical waters and the North Pacific subtropical gyre. The Northwest Pacific Ocean was a significant source of atmospheric NMHCs, with average sea-to-air fluxes of 28.0 ± 38.9, 65.2 ± 73.3, 21.0 ± 26.7, 48.7 ± 62.6, 12.7 ± 15.9, 14.2 ± 16.8, and 41.7 ± 80.4 nmol m-2 d-1 for ethane, ethylene, propane, propylene, i-butane, n-butane, and isoprene, respectively. Influenced by seawater release and OH radical consumption, the atmospheric NMHCs apart from isoprene displayed upward trends with increasing latitude. The deck incubation showed that the addition of aerosols and acidic aerosols significantly boosted phytoplankton biomass, altered community structure, and accelerated the production of isoprene. However, the other six NMHCs showed no obvious responses to atmospheric aerosol deposition in the incubation experiments. In summary, ocean current movements and atmospheric deposition could influence the production and release of isoprene in the Northwest Pacific Ocean.

Carbonate chemistry variability in the southern Yellow Sea and East China Sea during spring of 2017 and summer of 2018.

Marginal seas are highly productive and disproportionately large contributors to global air-sea CO2 fluxes. Due to complex physical and biogeochemical conditions, the southern Yellow-East China Sea is an ideal site for studying carbonate chemistry variability. The carbonate system was investigated in the area in spring of 2017 and summer of 2018. Dissolved inorganic carbon (DIC) and total alkalinity (TA) concentrations were higher in the SYS than the ECS due to material from carbonate weathering and erosion carried by the Yellow River. High pH and low DIC and TA were observed in the Zhe-Min Coastal Current in spring due to high primary productivity caused by Changjiang River input and the Taiwan Warm Current. Temperature and biological activity were the primary drivers controlling the partial pressure of CO2 (pCO2) in the SYS, pCO2 was controlled by primary productivity related to nutrients carried by the Changjiang River and physical mixing in the Changjiang River plume and inner/middle shelves of the ECS, whereas temperature was the dominant factor determining pCO2 distributions in the ECS outer shelf waters influenced by the Kuroshio Current. Overall, the entire study area shifted from a CO2 sink (-4.18 ± 5.60 mmol m-2 d-1) to a weak source (1.02 ± 4.87 mmol m-2 d-1) from spring to summer. Specifically, the SYS and ECS offshore waters changed from CO2 sinks in spring to sources in summer, while the Changjiang River plume was always a CO2 sink.

Anthropogenic impacts on nutrient variability in the lower Yellow River.

Excessive nutrient discharges and changes in nutrient ratios caused by global change and anthropogenic activities have been reported in global rivers; however, the actual alterations occurring in the Yellow River environment is too fast to catch up with. From 2001 to 2018, dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP) and dissolved silicon (DSi) concentrations showed decreasing trends in the lower Yellow River throughout the study period. Dissolved organic phosphorus (DOP) concentrations increased since 2009, reaching up to 95% of the total dissolved phosphorus. Annual minimum dissolved organic nitrogen concentrations increased with time. We observed extremely low nutrient concentration events since 2014 in response to the retention effect of large reservoirs; this significantly reduced the downstream water discharge and sediment load and increased phytoplankton uptake. To further analyze the variability of nutrient fluxes, we quantified the fluxes to the Yellow River from natural (runoff, precipitation deposition, and sediment load from the Loess Plateau), anthropogenic (recharged water, fertilizer application, and vegetation coverage), social and industrial (population urbanization, GDP, and sewage effluents) sources. The highest contributions of total nutrient fluxes emptied into the Yellow River was fertilizer losing (44-48%) for DIN, sewage effluents (85-88%) for DIP, and runoff (35-65%) for DSi, respectively. Strictly controlling the amount of fertilizer and improving the application methods, improving sewage treatment technology, and vigorously promoting "green travel" might reduce nutrients emptied into the Yellow River based on the main sources of nutrients. Our study may help policy makers formulate strategies and it is possible to own a better water quality in the Yellow River.

[Distribution and Emission of Nitrous Oxide (N2O) in Three Gorges Reservoir and Downstream River].

Nitrous oxide (N2O) is an important greenhouse gas and has a great impact on global warming. Affected by human activities, rivers, and reservoirs have become active sites for N2O production and emission. In Three Gorges Reservoir and the downstream Yangtze River, the concentrations and fluxes of dissolved N2O were investigated in September-October 2009 and October 2016 to identify the factors controlling the distribution of N2O in the reservoir and the effect of damming and reservoir operation on N2O emission from the Yangtze River. The dissolved N2O concentration of the reservoir ranged from 9.74 to 16.36 nmol·L-1 with an average of (12.49±1.75) nmol·L-1 in the surface water (about 0 m) and ranged from 9.99 to 14.00 nmol·L-1 with an average of (11.21±0.91) nmol·L-1 in the bottom water (ranging from 6 m to 103 m). The dissolved N2O in the water column of Three Gorges Reservoir varied little, and no significant difference was noted between the overall N2O concentration in the reservoir and that in the downstream river. A positive correlation was noted between N2O and nitrate (NO3-) (P<0.01), although negative correlations were found between N2O and ammonium (NH4+) (P<0.05) and nitrite (NO2-) (P<0.01) in Three Gorges Reservoir. The surface N2O in the Three Gorges Reservoir was overall saturated, with saturation ranging from 122% to 170% in 2009 and from 114% to 187% in 2016. The mean emission rate of N2O from the surface water was (4.6±2.4) µmol·(m2·d)-1 in 2016 and (16.6±4.9) µmol·(m2·d)-1 in October 2009. The Three Gorges Reservoir is a non-negligible source of atmospheric N2O. No obvious difference was noted between upstream and downstream N2O concentrations, which implies that no degassing emission occurs when water passes through turbines and spillways.

Distribution and emission of N2O in the largest river-reservoir system along the Yellow River.

Rivers and reservoirs are affected by human activities and are sources of the greenhouse gas nitrous oxide (N2O). Concentrations of N2O in the middle and lower reaches of the Yellow River and Xiaolangdi Reservoir, China, were measured in June and December 2017. Fluxes were estimated by boundary layer method to explore their controlling factors, especially the impact of damming and reservoir operation. In the middle and lower reaches of the Yellow River, N2O concentrations in surface waters were 26.65 ±â€¯14.67 nmol L-1 in summer and 21.16 ±â€¯5.35 nmol L-1 in winter. In comparison, the concentrations of N2O in the reservoir were 32.94 ±â€¯17.32 nmol L-1 in summer and 23.73 ±â€¯5.60 nmol L-1 in winter. The longitudinal distribution of N2O along the river exhibited different patterns with surface N2O decreasing downstream towards the dam in summer but increasing in winter. Vertical profiles of N2O concentrations in the reservoir showed an increase with depth in summer but were almost vertically uniform in winter. In winter, N2O that had accumulated in the bottom water in summer was transported to the surface by vertical mixing and released into the atmosphere. Dissolved oxygen (DO), water temperature, and in situ biological production were the main factors affecting the distribution of N2O. The mean emissions rates of N2O from the surface waters were 13.7 ±â€¯8.8 µmol m-2 d-1 in summer and 13.2 ±â€¯7.6 µmol m-2 d-1 in winter. Approximately 1.31 × 106 mol N2O was released from the reservoir surface in 2017, which represents 0.12% of the annual N2O emissions from global reservoirs. The construction of dams increased N2O emission from the lower reaches of the river by 4.53 × 105 mol and 1.22 × 105 mol due to the discharge of the bottom water and the water and sediment regulation, respectively. This study demonstrates that the construction of dams and reservoir operation practices have made the Xiaolangdi Reservoir a key area for N2O emissions.

miR-149 reverses cisplatin resistance of gastric cancer SGC7901/DDP cells by targeting FoxM1.

Drug resistance remains a major unresolved obstacle for gastric cancer (GC) treatment. Recently, increasing studies have showen that microRNAs (miRNAs) are involved in cancer chemotherapeutic resistance and can potentially be applied to reverse drug resistance in cancers. The relationship between miRNA-149 expression and cisplatin (DDP) resistance in GC cells is still unknown. Here, we detected miR-149 expression by using RT-PCR and found that expression of miR-149 was downregulated in SGC7901/DDP cells compared with SGC7901cells, indicating a role of miR-149 in determining cisplatin-resistance of GC cells. Then, SGC7901/DDP cells were tansfected with miR-149 mimics, MTT assay was performed to determine SGC7901/DDP cell viability, and showed that overexpression of miR-149 inhibited the cell viability after cisplatin treatment, suggesting that up-regulation of miR-149 enhanced SGC7901/DDP cell sensitivity to cisplatin. Furthermore, we confirmed that Forkhead box M1 (FoxM1) is a direct target of miR-149 in SGC7901/DDP cells by using luciferase reporter assay. Besides, we also demonstrated that miR-149 enhances SGC7901/DDP cell sensitivity to cisplatin by downregulating FoxM1 expression. In summary, our data provide new insights that miR-149 plays an important role in determining sensitivity of cisplatin-resistant GC cells by targeting FoxM1 and suggest that miR-149 could be a potential target for reversing drug resistance in GC.

[Distributions and air-sea fluxes of dissolved nitrous oxide in the Yangtze River estuary and its adjacent marine area in spring and summer].

Distributions and air-sea fluxes of nitrous oxide (N2O) in the seawaters of the Yangtze River estuary and its adjacent marine area were investigated during two cruises in March and July 2012. Dissolved N2O concentrations in surface waters ranged from 9.34 to 49.08 nmol x L(-1) with an average of (13.27 ± 6.40) nmol x L(-1) in spring and ranged from 7.27 to 27.81 nmol x L(-1) with an average of (10.62 ± 5.03) nmol x L(-1) in summer. There was no obvious difference between surface and bottom N2O concentrations. N2O concentrations in both surface and bottom waters decreased along the freshwater plume from the river mouth to the open sea. High values of dissolved N2O were found in turbidity maximum zone, which suggests that maximal turbidity enhances nitrification. Temperature had dual effects on dissolved N2O concentrations. N2O saturations in surface waters ranged from 86.9% to 351.3% with an average of (111.5 ± 41.4)% in spring and ranged from 111.7% to 396.0% with an average of (155.9 ± 68.4)% in summer. N2O were over-saturated at most stations. The sea-to-air fluxes of N2O were estimated to be (3.2 ± 10.9), (5.5 ± 19.3) and (12.2 ±52.3) µmol x (m2 x d)(-1) in spring and (7.3 ± 12.4), (12.7 ± 20.4) and (20.4 ± 35.9) µmol x (m2 x d)(-1) in summer using the LM86, W92 and RC01 relationships, respectively. The annual emissions of N2O from the Yangtze River estuary and its adjacent marine area were estimated to be 0.6 x 10(-2) Tg x a(-1) (LM86), 1.1 x 10(-2) Tg x a(-1) (W92) and 2.0 x 10(-2) Tg x a(-1) (RC01). Although the area of the Yangtze River estuary and its adjacent marine area only accounts for 0.02% of the total area of the world's oceans, their emission of N2O accounts for 0.06% of global oceanic N2O emission, indicating that the Yangtze River estuary and its adjacent marine area is an active area to produce and emit N2O.

[Distribution and air-sea fluxes of methane in the Yellow Sea and the East China Sea in the spring].

A survey was carried out in the Yellow Sea and the East China Sea from March 17 to April 06 of 2011. Dissolved CH4 in various depths were measured and sea-to-air fluxes were estimated. Methane concentrations in surface and bottom waters ranged between 2.39-29.67 nmol x L(-1) and 2.63-30.63 nmol x L(-1), respectively. Methane concentrations in bottom waters were slightly higher than those in surface waters, suggesting the existence of methane source in bottom waters or sediments. The horizontal distribution of dissolved CH4 showed a decrease from the river mouth to the open sea, and was influenced by the freshwater discharge and the Kuroshio intrusion. Surface methane saturations ranged from 93%-1 038%. Sea to air CH4 fluxes were (2.85 +/- 5.11) micromol x (m2 x d)(-1) (5.18 +/- 9.99) micromol x (m2 x d)(-1) respectively, calculated using the Liss and Merlivat (LM86), the Wanninkhof (W92) relationships and in situ wind speeds, and estimated emission rates of methane from the East China Sea and the Yellow Sea range from 7.05 x 10(-2) - 12.0 x 10(-2) Tg x a(-1) and 1.17 x 10(-2) - 2.20 x 10(-2) Tg x a(-1), respectively. The Yellow Sea and East China Sea are the net sources of atmospheric methane in the spring.

[Distributions and pollution status of heavy metals in the suspended particles of the estuaries and coastal area of eastern Hainan].

The distributions and pollution status of heavy metals in the suspended particles were investigated in the Wanquan and Wenchang/Wenjiao estuaries and the coastal area of eastern Hainan in July 2008. The concentrations of metal elements (Al, Fe, Mn, Cr, Cu, Ni, V, Zn) were determined by ICP-AES after microwave digestion. Multivariate statistical methods (e. g. correlation analysis and principal factor analysis) were used to discuss the major factors controlling the variability of heavy metal concentrations and the pollution status in those areas. There was an obvious variability in particulate metal concentrations from upstream to estuary of both rivers. The concentrations first increased with increasing salinity and then decreased with further increase of the salinity; the concentrations were slightly higher at the coastal area in the east. The variability of particulate metal concentrations reduced significantly after the normalization by Al, indicating the effects of grain size. Enrichment factor calculation results showed that there was heavy metal pollution (especially Cu, Ni) in the Wenchang/Wenjiao River and estuary, while the situation in Wanquan River remained at pristine level. Concentrations of particulate metals in the study area were mainly controlled by source geology and provenance, as well as contamination from the discharge of waste water and biological activity.

[Distributions and seasonal variations of total dissolved inorganic arsenic in the estuaries and coastal area of eastern Hainan].

The concentrations of total dissolved inorganic arsenic (TDIAs) were measured by Hydride Generation-Atomic Fluorescence Spectrometry (HG-AFS). Two cruises were carried out in the river, estuary, coastal area and groundwater of eastern Hainan in December 2006 and August 2007. The concentrations of TDIAs in the Wanquan and Wenchang/Wenjiao rivers and their estuaries, coastal area in December 2006 were 4.0-9.4, 1.3-13.3, 13.3-17.3 nmol x L(-1), respectively. The concentrations of TDIAs in the Wanquan and Wenchang/Wenjiao rivers and their estuaries, coastal area in August 2007 were 1.6-15.5, 2.4-15.9, 10.8-17.6 nmol x L(-1), respectively. There was no significantly seasonal variation of TDIAs in the rivers and estuaries during the dry and wet seasons. Compared with other areas in the world, the concentration of TDIAs in the Eastern Hainan remained at pristine levels. TDIAs showed conservatively mixing in the both estuaries. The concentration of TDIAs of groundwater was below detection limit (BDL)-41.7 nmol x L(-1). The submarine groundwater discharge (SGD) to the coastal area was estimated in the drainage basin of Wenchang/Wenjiao river based on the average concentration of TDIAs in the groundwater and SGD water discharge, with the value of 1 153 mol x a(-1). Budget estimation indicated that the SGD discharge is one of the important sources of arsenic in the coastal area.

[Influence of Ruditapes philippinarum aquaculture on benthic fluxes of biogenic elements in Jiaozhou Bay].

Nutrient excretion rates and the impact of Ruditapes philippinarum on benthic nutrient fluxes were measured by incubation experiments, and these results were used to assess the effect of R. philippinarum aquaculture on nutrient recycling in Jiaozhou bay. Our research indicates that the bioturbation of R. philippinarum would modify biogeochemical progresses in sediment, and restrain nutrients excreted by R. philippinarum releasing to overlying water. Only 37% DIN and 34% PO4(3-) -P excreted by R. philippinarum were released to seawater across the sediment-water interface due to bioturbation of R. philippinarum. According to the reduction of nutrient exchange across the sediment-water interface by bioturbation, only 19% (N) and 17% (P) of biogenic elements fed by R. philippinarum can be recycled and returned to seawater, while the others would be removed from seawater in Jiaozhou Bay. The ratios of Si: N and Si: P of nutrients released from sediment to seawater with bioturbation of R. philippinarum were about 5:18 and 5:1, which were far less than Redfield ratios. Therefore, aquaculture of R. philippinarum should promote BSi biodeposition to sediment and reduce the nutrient ratios of Si: N and Si: P in seawater of Jiaozhou bay.

A triclinic polymorph with Z = 3 of N,N'-bis-(2-pyrid-yl)oxamide.

The asymmetric unit of the title compound, C(12)H(10)N(4)O(2), contains three half-mol-ecules. Each half-mol-ecule is completed by crystallographic inversion symmetry. The title compound, (I), is a polymorph of the structure, (II), reported by Hsu & Chen [Eur. J. Inorg. Chem. (2004), 1488-1493]. In the original report, the compound crystallized in the tetra-gonal space group P[Formula: see text]2(1)c (Z = 8), whereas the structure reported here is triclinic (P[Formula: see text], Z = 3). In both forms, each oxamide mol-ecule is almost planar (with maximum deviations are 0.266 and 0.166 Å) and the O atoms are trans oriented. The principal difference between the two forms lies in the different hydrogen-bonding patterns. In (I), two N-H⋯O and one N-H⋯N hydrogen bonds link the mol-ecules, forming a two-dimensional network, whereas in (II) there are no classical hydrogen bonds to O atoms and only weak C-H⋯O inter-actions are found along with rings of N-H⋯N bonds.

[Distribution and emission of methane from the Changjiang].

Field surveys along the Changjiang were carried out in January 2008 and September 2008, persistently. Monthly survey at Xuliujing of the Changjiang Estuary was carried out from September 2007 to August 2008. Concentrations of methane in the Changjiang were measured by purge and trap-gas chromatography and the atmospheric methane fluxes were calculated according to the equation by Wanninkhof. The mean concentration in surface waters of the Changjiang was (330.8 +/- 186.9) nmol x L(-1) in January 2008 and (80.9 +/- 58.3) nmol x L(-1) in September 2008, persistently. Concentrations in bottom waters were consistent with those in surface waters. Supersaturated in methane with an average air-water flux of (385.1 +/- 278.0) micromol x (m2 x d)(-1). Besides, average methane concentration at Xuliujing was (167.5 +/- 91.4) nmol x L(-1) with an average air-water flux (690.9 +/- 291.6) micromol x (m2 x d)(-1), the high values appeared in February and July. Along the middle reaches of the Yangtze River, methane concentrations were increased, and the lower reaches were reduced. In the estuary, methane concentrations decreased rapidly from Xuliujing to the sea, showed negative correlation with salinity. The input of CH4-rich water form tributaries and lakes impacted the methane concentration trend of the Changjiang. The Changjiang was estimated to contribute 208 Gg CH4 to the atmosphere annually. However, the freshwater CH4 discharge to the East China Sea was 112 x 10(6) mol x a(-1) in the estuary.

Theoretical studies on the reactions CH3SCH3 with OH, CF3, and CH3 radicals.

The multiple-channel reactions OH + CH(3)SCH(3) → products, CF(3) + CH(3)SCH(3) → products, and CH(3) + CH(3)SCH(3) → products are investigated by direct dynamics method. The optimized geometries, frequencies, and minimum energy path are all obtained at the MP2/6-31+G(d,p) level, and energetic information is further refined by the MC-QCISD (single-point) method. The rate constants for eight reaction channels are calculated by the improved canonical variational transition state theory with small-curvature tunneling contribution over the temperature range 200-3000 K. The total rate constants are in good agreement with the available experimental data and the three-parameter expressions k(1) = 4.73 × 10(-16)T(1.89) exp(-662.45/T), k(2) = 1.02 × 10(-32)T(6.04) exp(933.36/T), k(3) = 3.98 × 10(-35)T(6.60) exp(660.58/T) (in unit of cm(3) molecule(-1) s(-1)) over the temperature range of 200-3000 K are given. Our calculations indicate that hydrogen abstraction channels are the major channels and the others are minor channels over the whole temperature range.

Environmental change in Jiaozhou Bay recorded by nutrient components in sediments.

Inorganic or bulk organic chemical indicators, including organic carbon (OC), total nitrogen, organic nitrogen (ON), fixed ammonium (N(fix)), exchangeable ammonium, exchangeable nitrate, organic phosphorus (OP), inorganic phosphorus (IP), and biogenic silica (BSi), were examined in a 3-m core collected in Jiaozhou Bay (JZB) to decipher how the environment has changed during the preceding two centuries of increasing anthropogenic influence in this region. Concentrations of BSi, OC, and OP reveal overall increases to ca.30 cm ( approximately 1984), then decreased toward the surface, probably reflecting a decrease in the productivity of overlying waters since 1984. Aquaculture might play an important role in the decrease of nutrient elements in the upper layers recorded in sediments. The decreased molar BSi/OC ratios upcore may be due to a change in dominance from large- to small-sized diatoms, as shown in other research. However, the shift may also be related to changes from heavily-silicified to lightly-silicified diatoms or to non-siliceous forms such as dinoflagellates. ON concentrations increased towards the surface sediment, which is most likely consistent with the increase in fertilizer application and wastewater discharge. Concentrations of IP, total P, and N(fix) all decreased conspicuously upcore at 41 cm depth ( approximately 1977), and were largely consistent with the decrease in rainfall and freshwater discharge to JZB. Our data suggest that the environment has significantly changed since the 1980s. Anthropogenic activities in the watersheds may exert a substantial influence on carbon cycling processes in estuaries and potentially the coastal ocean.

Theoretical study and rate constants calculation for the reactions of SiH3 radical with SiH3CH3 and SiH2(CH3)2.

The multiple-channel reactions SiH(3) + SiH(3)CH(3) --> products and SiH(3) + SiH(2)(CH(3))(2) --> products are investigated by direct dynamics method. The minimum energy path (MEP) is calculated at the MP2/6-31+G(d,p) level, and energetic information is further refined by the MC-QCISD method. The rate constants for individual reaction channels are calculated by the improved canonical variational transition state theory (ICVT) with small-curvature tunneling (SCT) correction over the temperature range of 200-2400 K. The theoretical three-parameter expression k(1)(T) = 2.39 x 10(-23)T(4.01)exp(-2768.72/T) and k(2)(T) = 9.67 x 10(-27)T(4.92)exp(-2165.15/T) (in unit of cm(3) molecule(-1) s(-1)) are given. Our calculations indicate that hydrogen abstraction channel from SiH group is the major channel because of the smaller barrier height among eight channels considered.

[Seasonal variations of fluxes and distributions of dissolved N2O in the North Yellow Sea].

The concentrations and air-sea fluxes of dissolved N2O were investigated in the North Yellow Sea during March 2005, April and August 2006, April and October 2007. Seasonal variations of dissolved N2O concentrations (about 12 nmol x L(-1)) in the North Yellow Sea were not obvious. The saturations of dissolved N2O in the North Yellow Sea showed obvious seasonal variations with higher values occurring in summer and autumn and lower in spring, and the dissolved N2O of the surface water was from undersaturated to oversaturated with the water temperature gradually increasing during three cruises in Spring. The correlation analysis shows that temperature was the main factor to influence N2O saturations. The estimated average N2O fluxes using the Liss and Merlivat (LM86) and Wanninkhof formula (W92) were (0.6 +/- 1.7), (5.8 +/- 8.4), (7.9 +/- 8.2) micromol x (m2 x d)(-1) and (1.1 +/- 2.7), (10.2 +/- 13.6), (13.8 +/- 14.3) micromol x (m2 x d)(-1), respectively, for spring, summer and autumn. Air-sea fluxes of dissolved N2O showed obvious seasonal variations, with the N2O fluxes of summer and autumn higher than those of spring. Based on the average annual N2O flux and the area of the North Yellow Sea, the annual N2O emission from the studied area was estimated to be (5.3 x 10(-3) -9.2 x 10(-3)) Tg x a(-1). From the above results, it can be seen that the North Yellow Sea was a net source of atmospheric N2O.

Simultaneous determination of herbicide mefenacet and its metabolites residues in river water by solid phase extraction and rapid resolution liquid chromatography-mass spectrometry with pre-column derivatization.

A procedure based on solid phase extraction (SPE) has been developed for the simultaneous pre-concentration of herbicide mefenacet (MN) and its three photolysis degradation products. Three metabolites studied were hydroxylbenzothiazole (HBT), N-methylaniline (N-MA) and 2-benzothiazoloxyacetic acid (2-BAA). A trimethylsilylation derivatization method was applied for the analysis of HBT and 2-BAA which were derivatized to be corresponding derivatives D-1 and D-2, respectively, and a rapid resolution liquid chromatography-electrospray ionization mass spectrometry (RRLC-ESI-MS) system was used for the separation, identification and quantification of these four analytes. In the SPE pre-concentration step, three types of cartridges and four kinds of eluents were investigated. The mean recoveries of these four analytes were between 78.6% and 101.2% and relative standard deviations were between 3.2% and 9.2%. The limits of detection (LODs) obtained were 0.02 ng l(-1) for MN and N-MA and 0.1 ng l(-1) for HBT and 2-BAA which were less than the maximum residue limits (MRLs) in drinking water established by European legislation (0.1 microg l(-1)). The proposed method was applied to evaluate the presence and evolution with time of herbicide mefenacet and its degradation products in samples of Songhuajiang River of Heilongjiang province, China. The analyses, conducted from April to July of 2008, pointed to the presence of MN, 2-BAA, HBT and N-MA at maximum levels 1.0, 0.08, 0.1 and 0.3 microg l(-1).

Theoretical study on the reaction of SiH(CH(3))(3) with SiH(3) radical.

The multiple-channel reactions SiH(3) + SiH(CH(3))(3) --> products are investigated by direct dynamics method. The minimum energy path (MEP) is calculated at the MP2/6-31+G(d,p) level, and energetic information is further refined by the MC-QCISD (single-point) method. The rate constants for individual reaction channels are calculated by the improved canonical variational transition state theory with small-curvature tunneling correction over the temperature range of 200-2400 K. The theoretical three-parameter expression k(T) = 2.44 x 10(-23)T(3.94) exp(-4309.55/T) cm(3)/(molecule s) is given. Our calculations indicate that hydrogen abstraction channel R1 from SiH group is the major channel because of the smaller barrier height among five channels considered.

Theoretical study on the OH + CH3NHCOOCH3 reaction.

The multiple-channel reactions OH + CH3NHC(O)OCH3 --> products are investigated by direct dynamics method. The optimized geometries, frequencies, and minimum energy path are all obtained at the MP2/6-311+G(d,p) level, and energetic information is further refined by the BMC-CCSD (single-point) method. The rate constants for every reaction channels, R1, R2, R3, and R4, are calculated by canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200-1000 K. The total rate constants are in good agreement with the available experimental data and the two-parameter expression k(T) = 3.95 x 10(-12) exp(15.41/T) cm3 molecule(-1) s(-1) over the temperature range 200-1000 K is given. Our calculations indicate that hydrogen abstraction channels R1 and R2 are the major channels due to the smaller barrier height among four channels considered, and the other two channels to yield CH3NC(O)OCH3 + H2O and CH3NHC(O)(OH)OCH3 + H2O are minor channels over the whole temperature range.