Preferences for pre-exposure prophylaxis for HIV: A systematic review of discrete choice experiments.

Background: We aimed to systematically review the health preference literature using discrete choice experiments (DCEs), an attribute-based stated preference method, to investigate patient preferences for HIV pre-exposure prophylaxis (PrEP). Methods: A search in PubMed, Scopus, CINAHL, and Embase was conducted on July 1, 2021, and updated on November 3, 2021. We used two concepts to create our search strategy: (1) discrete choice experiments/conjoint analysis/best-worst scaling, and (2) HIV PrEP.The study is registered in PROSPERO (CRD42021267026). Findings: In total, 1060 studies were identified, and 18 were included in the analysis. Various attributes were examined, including dosing regimen, type of PrEP products, side effects, other side benefits, cost, effectiveness, dispensing venue, and additional support services. Dosing frequency, cost, the effectiveness of PrEP, dispensing venue, and side effects were the most common attributes examined in DCEs. Despite significant heterogeneity in preferences across subpopulations, overall, the most important attributes were cost (28%, 5/18), effectiveness (28%, 5/18) followed by dosing frequency (17%, 3/18). Interpretation: Notably, in studies where all of these three attributes were examined, some individuals would trade effectiveness for cost or vice versa. Ensuring PrEP is low cost or free, widely disseminating information of its effectiveness and advancements in reducing dosing frequency could accelerate the uptake of PrEP for those who would benefit from PrEP the most. Funding: None.

[Dynamic Changes in Hydrochemical Characteristics and Influencing Factors in the Karst Watershed Flood Process].

The hydrochemistry of river water in a karst basin has a rapid response to the rainstorm/flood process, which is an important process of the karst carbon cycle and should not be ignored. Based on the dynamic monitoring of the hydrochemical characteristics of the flood process in the Yangshuo section on November 8-12, 2015, the dynamic change in the main ions and the influencing factors were analyzed, and the concentration and flux of inorganic carbon from different sources were calculated. The results showed that the hydrochemistry types in different stages of the flood area belonged to the Ca-HCO3 type. The ions were mainly sourced from carbonate weathering, and affected by silicate weathering, rainfall, and human activities. Because of the hydrological process, the weathering strength of carbonate rocks sharply weakened at the beginning of the flood, and then gradually increased. The concentrations of HCO3-, Ca2+, and Mg2+ sharply decreased at the beginning of the flood, then gradually increased, and continued to increase in the second flood process because of the waterlogging in the karst system. Because of the waterlogging, the reaction time between water and rock become longer; thus, the concentrations are higher. The dynamic changes in SO42-, Cl-, Na+, and K+ were mainly affected by precipitation and human activities. At the beginning of the flood, the concentrations of SO42-, Cl-, Na+, and K+ increased because the runoff takes more ions sourced from activities. The concentrations of SO42-, Cl-, Na+, and K+ decreased with the decrease of easily transported substances. At the lowest point of concentration, SO42- and Cl- were mainly sourced from precipitation, and Na+ and K+ were mainly sourced from precipitation and silicate weathering. The weathering of carbonates by carbonic acid was the main source of inorganic carbon, accounting for 74.3% of total inorganic carbon on average. Because of the input of sulfuric/nitric acid, the contribution of the weathering of carbonates by sulfuric/nitric acid to the inorganic carbon cannot be ignored, and the contribution increased significantly in the flood, up to 31.7%. The geological carbon sinks before the flood, and during the first and second flood processes in the Yangshuo section were 1.28×108, 5.28×108, and 11.52×108 g·d-1, respectively. The geological carbon sink before the flood was equal to the annual average flux, whereas the geological carbon sink in the flood process was several times that of the annual average flux. Moreover, because of the significant difference in the weathering strength of carbonate rocks during the two floods, there was also a significant difference in the amount of geological carbon sink under the same discharge.

[Fate and Origin of Major Ions in River Water in the Lhasa River Basin, Tibet].

In order to understand the temporal and spatial variations of major ions in water and their sources in the Lhasa River Basin, water samples were collected monthly at the hydrological station in the Lhasa River from August 2014 to July. The results show that HCO3- is the dominant anion in the water of the Lhasa River, which accounts for 68.73% of the anions, followed by SO42-. Ca2+ is the dominant cation, which accounts for 67.75% of the cations, followed by Mg2+. The pH values of the river water range between 8.31 and 8.90, with a mean of 8.59 throughout the year, generally showing alkaline water. The highest pH values occur in summer, which is probably due to the photosynthesis of aquatic plants and the growth of phytoplankton. Electrical conductivity (EC) varies between 155.0 and 257.0 µS·cm-1, with a mean of 210.5 µS·cm-1. Because of the frequent uplift of the Tibetan Plateau that enhanced the mechanical weathering of rocks and mineral dissolution, the total dissolved solid (TDS) concentration, at an average of 181.35 mg·L-1, is significantly higher than the average value of rivers around the world. The Lhasa River is recharged by surface runoff, so the concentrations of major ions in water are higher during winter, but lower in summer. An ion source analysis indicates that Ca2+, Mg2+, and HCO3- are mainly derived from chemical weathering of carbonate minerals, Cl-, SO42-, and NO3- are mainly affected by precipitation and rock weathering. Furthermore, the concentrations of major ions in the water have a negative correlation with the river discharge rate, which suggests there might be a dilution effect occurring during the rainy season.

[Spatial Variation and Environmental Significance of δ18O and δD Isotope Composition in Xijiang River].

The H and O isotope composition of the Xijiang water was investigated on 54 samples collected from the mainstreams and main tributaries in June 2014 and January 2015.It was found that in the Xijiang river, there was a remarkable linear relationship between δ18 O and δD. This relationship was more significant in the dry season. In both seasons, the 18 O and D values distributed along the meteoric water line, which indicated that precipitation was the source of the Xijiang River. Due to the direct water recharge through karst forms (i.e. sinkholes, vertical shaft and funnel) to the underground river, the d-excess value was higher in the rainy season. While during the dry season, water recharge came from the storage in fissures and pores. Affected by altitude and evaporation effect, along the mainstream Hongshui River-Xunjiang and tributary Youjiang-Yujiang reach, the δ18 O and δD values were gradually approaching positive value in general. However, along the short tributary Guijiang reach, the altitude difference was not dramatic, and the discharge was less, the same phenomenon was not observed. By establishing a linear regression model between δ18 O and altitude, it revealed that the change rate of Xijiang water with altitude was -0.44‰·(100 m)-1 in the rainy season, and -0.45‰·(100 m)-1 in the dry season. The result reflected the height effect of the precipitation, which has a considerable meaning for the study of hydrological cycle in a river basin.

[Hydrochemical Characteristics and Influencing Factors in Different Geological Background: A Case Study in Darongjiang and Lingqu Basin, Guangxi, China].

The observation and sampling were carried out in May 2013 to April 2014 in a hydrological year for two river basins with different geological background in upstream of Li river basin. The seasonal variations of river water chemistry and its main influencing factors were discussed in this paper. The results showed that the hydrochemistry types of both Darongjiang basin with 9% of carbonates and Lingqu basin with nearly 50% of carbonates in area belonged to Ca-HCO3 type. Ca2+ and HCO3- were the main cations and anions. The main ion concentrations were higher in winter and lower in summer, affected by the change of the flow. Ca2+, Mg2+, HCO3- were mainly sourced from the weathering of carbonates by carbonic acid. The weathering of carbonates by sulfuric acid and the weathering of silicate rocks also had contribution to the river water chemistry. In addition, comparing to the Lingqu basin, the contribution of the weathering of carbonates was much more than the percent of carbonates area, because the carbonate rocks were eroded by the allogenic water. On the other hand, K+, Na+, Cl-, NO3-, SO4(2-) were mainly affected by the atmospheric precipitation and human activities. Comparing to the Darongjiang Basin, the effects of human activities on the changes of K+, Na+, Cl-, NO3-, SO4(2-) were more significant in Lingqu Basin.

[Hydrochemical Characteristics and the Dissolved Inorganic Carbon Flux in Liuzhou Section of Liujiang Basin].

An important aspect of the current global change research is using river chemical composition to reveal the chemical weathering process and its effect of carbon sink. In this study, water samples were collected and analyzed 2 ~3 times per month from January to December in 2013. The hydrochemistry belonged to HCO3-Ca type. Ca+ and HCO3- were the main cation and anion, which reflected that the hydrochemical characteristics of river were mainly affected by the dissolution of carbonate rock. The concentration of main ions varied with the seasons, which reflected that the crest value occurred in winter, followed by those in autumn and spring, and the lowest value was observed in summer. Due to the interaction of effect of dilution and effect of C2, the seasonal variation of Ca2+ and HCO3- showed that the highest value was in autumn and the lowest value was in summer. The seasonal variation law of other ions should be attributed to the effect of dilution or agricultural activities or combined action of them. Both carbonic acid and sulfuric acid took part in the chemical weathering of carbonate rocks as evidenced by stoichiometric analysis. Besides, the δ34S of sulfate ion of the river waters (δ34S: from 7. 65 per thousand to 8. 55 per thousand) showed that SO2- was originated mainly from oxidation of sulfide minerals in ore deposits and acid rain. Chemical mass balance method was applied to estimate the proportion of HCO- coming from carbonate weathering by sulfuric acid. The result was 28. 26% . On this basis, the total carbon flux of carbon ( by CO2 calculation) in Liuzhou section calculated month by month was about 8. 95 x 10(5) t . a-1. What's more, the carbon flux showed a positive correlation with flow, which implied that the discharge of catchment was the main influencing factor of carbon flux rather than the HCO3- concentration.

[Effect of hydrochemistry characteristics under impact of human activity: a case study in the upper reaches of the Xijiang River basin].

In this paper, observation and sampling were taken three times a month in a hydrological year for three typical sections of the middle and upper reaches of the Xijiang River basin, based on the data of hydrochemistry and flow, the article mainly discusses the evolution process of hydrochemistry in river under natural process and impact of human activity. Hydrochemical characteristics of 116. samples were analyzed in the study area. The hydrochemistry type in the middle and upper reaches of the Xijiang River basin belonged to HCO3- -Ca2+ type, and the chemical weathering type mainly came from carbonate rock weathering. Ca2+ and HCO3- were the main cations and anions, which reflected that hydrochemical characteristics of river in karst area mainly affected by the dissolution of carbonate rock. Na, Mg2, Ca2+ and Cl- mainly affected by natural conditions, the impact of human activity was little. K+, NO3-, SO4(2-) and HCO3- were affected by human activity in different degrees, and it showed different influence ways. This study had an important significance for the change of river hydrochemistry, water quality characteristics, and the effect on substance transported fluxes in the downstream of Pearl River and water quality protection in South China Monsoon Area.

[Diel variations of hydrochemistry and influencing factors in a surface stream in subtropical karst area, SW China].

In order to understand the diel variation and influencing factors of hydrochemistry in a surface creek fed by karst subterranean river in a subtropical area, where is located at Guancun Village, Daliang Township, Rong'an County of Guangxi Zhuang Autonomous Region, China, two monitoring sites were set simultaneously to launch Guancun subterranean river outlet (G1) and surface creek mouth (G2), respectively. Physical and hydrochemical parameters including pH, dissolved oxygen (DO), water temperature (T) and specific conductivity (Spc) were measured at 15-minute intervals and water samples for analyzing major ions such as Ca2+, HCO3- and NO3- as well as delta3C(DIC) were collected at 2-hour intervals. The results showed that: (1) G1 and G2 sites were both HCO3- Ca type water, however the two monitoring sites showed different diel variations of hydrogeochemical process; (2) The physical and hydrochemical parameters (T, DO, pH, Spc) and major ions (Ca2+, Mg2+, Na+, K+, HCO3-, SO4(2-), NO3-, Cl- in G1 site were basically stable, while the physical and hydrochemical parameters (T, DO, pH, Spc) and major ions (Ca2+, HCO3- and NO3-) in G2 site displayed regular diel variation during monitoring; (3) The dissolved inorganic carbon (DIC) and delta13C values in G2 monitoring site showed reverse characteristics in diurnal fluctuations, where DIC decreased in daylight and increased at night while the delta13C value increased in daylight and decreased at night, DIC also showed a negative correlation with the delta13C value (correlation coefficient is -0. 87, P < 0.01) in G2 site. These results indicated that photosynthesis and respiration of aquatic plants, water temperature and degassing jointly affected diurnal variation of hydrochemistry and controlled the cycling process of internal matter in this surface creek fed by karst subterranean river.

[Contamination of polycyclic aromatic hydrocarbons in surface water in underground river of Dashiwei Tiankeng group in karst area, Guangxi].

In order to understand the composition, sources and contamination characteristics of PAHs in water from underground river of Dashiwei Tiankeng group in typical karst area located in Leye County, Guangxi. The water samples were collected from different sections to analyze 16 priority polycyclic aromatic hydrocarbons using GC-MS. The results showed that concentration of Sigma PAHs (the total PAHs) in water ranges from 54.7 ng/L to 192.0 ng/L, with an average concentration of 102.3 ng/L. The predominant PAHs in water are 2-3 ring PAHs, accounting for 65.1% of PAHs. The distribution of PAHs in water sampled along the underground river indicates that the mean concentration of PAHs in upstream area is higher than that of downstream because of wastewater discharge. Meanwhile, the underground river has some adsorption effect to 4-6 ring PAHs. The concentration of Sigma PAHs at Dashiwei Tiankeng section increases 93.8% attribute to the release of PAHs coming from Karst environmental medium and/or atmospheric transmission in underground river system. However, the concentration of Sigma PAHs at the confluence section of the tributary of Dashiwei Tiankeng is 47.3% less than that of the first upstream section duo to dilution. The concentration of Sigma PAHs at Bailang outlet section is 128.3% and 17.8% higher than that of flow-in section and Dashiwei Tiankeng section respectively. The ratios of specific PAHs indicate that the PAH sources in Leye County and Dashiwei Tiankeng areas mainly come from both petroleum and its combustion. However, the petroleum origin comes from anthropogenic inputs in town and the natural inputs in Dashiwei Tiankeng. The PAH sources in rural areas are mainly originating from the combustion of grass, wood and coal. Comparison to other areas in the world, the Sigma PAHs residual levels in underground river water in Dashiwei Tiankeng group is at the low level. In six sections, concentrations of benzo[a]pyrene (BaP) in surface water exceed the state quality standards.