Detecting interaction(s) and assessing the impact of component subsets in a chemical mixture using fixed-ratio mixture ray designs

An important environmental and regulatory issue is the protection of human health from potential adverse effects of cumulative exposure to multiple chemicals. Earlier literature suggested restricting inference to specific fixed-ratio rays of interest. Based on appropriate definitions of additivity, single chemical data are used to predict the relationship among the chemicals under the zero-interaction case. Parametric comparisons between the additivity model and the model fit along the fixed-ratio ray(s) are used to detect departure from additivity. Collection of data along reduced fixed-ratio rays, where subsets of chemicals of interest are removed from the mixture and the remaining compounds are at the same relative ratios as considered in the full ray, allow researchers to make inference about the effect of the removed chemicals. Methods for fitting simultaneous confidence bands about the difference between the best fitting model and the model predicted under additivity are developed to identify regions along the rays where significant interactions occur. This general approach is termed the “single chemicals required” (SCR) method of analysis. A second approach, termed “single chemicals not required” (SCNR) method of analysis, is based on underlying assumptions about the parameterization of the response surface. Under general assumptions, polynomial terms for models fit along fixed-ratio rays are associated with interaction terms. Consideration is given to the case where only data along the mixture rays are available. Tests of hypotheses, which consider interactions due to subsets of chemicals, are also developed.     

“Fertile island” effects of <Emphasis Type="Italic">Tamarix chinensis</Emphasis> Lour. on soil N and P stoichiometry in the coastal wetland of Laizhou Bay,China

Purpose

As a useful comprehensive index for reflecting nutrient cycling in soils, nitrogen (N) and phosphorus (P) stoichiometry is subject to influences of many external environmental and biological factors. Studies on such influences were limited, and the influential mechanism remains unclear. The purpose of this research is to investigate soil N and P stoichiometric variations and analyze “fertile island” effects of Tamarix chinensis Lour. (T. chinensis) in the coastal wetland of Laizhou Bay in China.

Materials and methods

Soil samples beneath clusters and communities of T. chinensis were collected respectively in July 2012. Amounts of ammonium, nitrate, and available phosphorus in the soil samples were measured through the corresponding standard methods for material measuring.

Results and discussion

In general, there were significant vertical variations in soil N and P stoichiometry beneath clusters and communities of T. chinensis. A downtrend was observed for N and P contents with the increase in soil depth. On the contrary, the N/P ratio revealed a trend of going up first and then dropping off along with the increase of the soil depth. Comparatively, the horizontal variations in the soil N and P stoichiometry beneath a single cluster of T. chinensis were greater in the topsoil than those in the subsoil. The N and P contents gradually decreased from the canopy center to the outside. On the contrary, an opposite trend was found for the N/P ratio. For the horizontal variations beneath T. chinensis communities, there were no significant differences for either N and P contents or N/P ratios.

Conclusions

Similar to the ecosystems in arid and semi-arid areas, vegetations in many semi-humid areas could also form fertile islands and exert significant influences on the soil nutrient cycle. The formation of fertile islands beneath a single cluster of T. chinensis could have significant influence on soil N and P stoichiometry. Under the influence of fertile islands beneath T. chinensis, the limiting element of the biogeochemical processes in the coastal wetland of Laizhou Bay might change from N to P. However, the influences of fertile island effects on soil N and P stoichiometry beneath T. chinensis communities were relatively small, illustrating that the influences of fertile island effects was not significant at the community level. Thus, the impacts of environmental factors on soil N and P stoichiometry might be greater than that of the fertile island effects in the wetland on a larger scale.

     

A novel heavy metal chelating agent sixthio guanidine acid for in situ remediation of soils contaminated with multielements: its synthesis,solidification, biodegradability,and leachability

Purpose

The main objectives of the study were to (1) develop a one-step facile procedure for synthesizing a new chemical amendment agent with three chelating groups for solidifying multiple heavy metals, called sixthio guanidine acid (SGA), using guanidine hydrochloride and carbon disulfide as raw reactants and (2) assess its biodegradability, solidification effectiveness, and leachability in remedying soils contaminated with multiple heavy metals of various concentrations compared with other traditional amendment agents.

Materials and methods

Polluted soil samples were collected near a metalliferous mining site of Qixiashan in the southeast of Nanjing, China. Their concentrations were determined at 22.15–320 mg kg^?1 for As, 3.30–29.31 mg kg^?1 for Cd, 115.66–158.65 mg kg^?1 for Ni, 165.04–1677.06 mg kg^?1 for Pb, and 355.6–2426.91 mg kg^?1 for Zn. Biodegradability of SGA was assessed in accordance with GB/T 21831-2008 and OECD-301D. Total concentration of heavy metals was determined according to ISO11466:1995. A modified three-step sequential Community Bureau of Reference (BCR) extraction procedure was used to examine speciation of heavy metals in the soil sample, and concentrations of heavy metals were measured by using inductively coupling plasma optical emission spectrometry (ICP-OES). Leachate extraction tests were carried out before and after the soil sample was solidified with different amendments in accordance with HJ/T 557-2009.

Results and discussion

It is found that the optimal conditions for SGA synthesis are a molar ratio of 4:1, a reaction temperature of 40 °C, and a reaction time of 2 h. Under such conditions, SGA yield is achieved as high as 91.5 %. The bioavailability and mobility of As, Cd, Ni, Pb, and Zn in highly contaminated soils can be reduced via using SGA. Our results indicate that SGA is nonbiodegradative and much more effective than other traditional chemical amendment agents in that it is highly effective in comprehensively solidifying As, Cd, Ni, and Pb.

Conclusions

SGA has the potential for comprehensive in situ remediation of soils contaminated with several heavy metal elements of various concentration levels, and such findings may be used as a guide to design new chemical amendment agents for rehabilitating soils contaminated with heavy metals.

     

Stability of soil organic carbon and potential carbon sequestration at eroding and deposition sites

Purpose

This study aims to explore the dynamics of the factors influencing soil organic carbon (SOC) sequestration and stability at erosion and deposition sites.

Materials and methods

Thermal properties and dissolved aromatic carbon concentration along with Al, Fe concentration and soil specific surface area (SSA) were studied to 1 meter depth at two contrasting sites.

Results and discussion

Fe, Al concentrations and SSA size increased with depth and were negatively correlated with SOC concentration at the erosion site (P?<?0.05), while at the deposition site, these values decreased with increasing depth and were positively correlated with SOC concentration (P?<?0.05). TG mass loss showed that SOC components in the two contrasting sites were similar, but the soils in deposition site contained a larger proportion of labile organic carbon and smaller quantities of stable organic carbon compared to the erosion site. SOC stability increased with soil depth at the erosion site. However, it was slightly variable in the depositional zone. Changes in SUVA₂₅₄ spectroscopy values indicated that aromatic moieties of DOC at the erosion site were more concentrated in the superficial soil layer (0–20 cm), but at the deposition site they changed little with depth and the SUVA₂₅₄ values less than those at the erosion site.

Conclusions

Though large amounts of SOC accumulated in the deposition site, SOC may be vulnerable to severe losses if environmental conditions become more favorable for mineralization in the future due to accretion of more labile carbon. Deep soil layers at the erosion site (>30 cm deep) had a large carbon sink potential.

     

Assessing chemical soil tests for predicting nitrogen mineralization in paddy soils of the Dongting Lake region in China

Purpose

Developing routine methods that accurately predict soil nitrogen (N) mineralization is essential for fertilization recommendation; thus, chemical soil testing has received worldwide attention. However, the optimal chemical soil test for predicting soil N mineralization is region specific. This study aimed to determine suitable chemical soil tests for predicting N mineralization in paddy soils of the Dongting Lake region, China.

Materials and methods

Composite surface samples (0–20 cm) of soils (n?=?30) with diverse inherent properties were collected from representative paddy fields across the region. The benchmark indices for soil N mineralization were the net mineralization rate of soil N in a 112-day anaerobic incubation under waterlogged conditions (NMRN₁₁₂) and N mineralization potential (N _o ) estimated using a modified double exponential model. Laboratory-based measurements of soil labile organic N (SLON) were conducted using chemical fractionation methods including 0.01 M NaHCO₃ extraction, hot 2 M KCl hydrolysis, phosphate-borate (PB) buffer hydrolysis, acidic KMnO₄ oxidation, and alkaline KMnO₄ oxidation. These were compared with the benchmark indices to assess their suitability for use as indicators for N mineralization.

Results and discussion

Acidic KMnO₄-oxidative organic N (acidic KMnO₄-N) and PB buffer-hydrolysable organic N (PB_HYDR-N) correlated strongly with NMRN₁₁₂ and N _o (r?=?0.825–0.884, P?<?0.001, n?=?30). Grouping of soils based on soil texture generally provided no improvement in the relationships of chemical soil tests with NMRN₁₁₂ and N _o . Multiple stepwise regression analysis indicated that combining acidic KMnO₄-N and PB_HYDR-N yielded the best prediction of soil N mineralization, explaining 86.1 and 85.5 % of the variation in NMRN₁₁₂ and N _o , respectively, of the 30 tested paddy soils.

Conclusions

The results of acidic KMnO₄-N and PB_HYDR-N as indicators for soil N mineralization were promising, and the operations of acidic KMnO₄ oxidation and PB buffer hydrolysis procedures are simple and cost-effective. Therefore, a combination of acidic KMnO₄-N and PB_HYDR-N shows promise in predicting N mineralization in paddy soils of the Dongting Lake region. However, further calibration through field studies is required and the chemical characteristics of acidic KMnO₄-N and PB_HYDR-N needs to be further clarified.

     

Incorporating LASSO effects into a mixed model for quantitative trait loci detection

The identification of quantitative trait loci (QTL) can be viewed as a subset selection problem. In a simulation study the least absolute selection and shrinkage operator (LASSO) is shown to be a useful and powerful tool for QTL identification. LASSO effects are embedded into a mixed model allowing simultaneous modeling of genetic and experimental effects. This provides the flexibility to model the experiment in conjunction with the power of LASSO QTL identification. Estimation is performed using an approximation to the restricted likelihood and modified Gaussian elimination. The extended mixed model is used to analyze a cattle gene mapping dataset.     

Arsenic,lead, and uranium concentrations on sediments deposited in reservoirs in the Rio Grande Basin,USA–Mexico border

Purpose

The El Granero reservoir is the last reservoir of the Rio Conchos before it joins the Rio Grande at the Mexico–USA border. This reservoir, together with the San Marcos reservoir, is located in the arid region of Chihuahua, Mexico. High, naturally occurring radioactivity levels, as well as high arsenic (As) concentrations, have been found in both reservoirs. The main goal of this research was to establish the spatial and temporal distribution of trace and radioactive elements in surface sediments and cores collected from these reservoirs.

Materials and methods

Sediment cores were dated using ²¹⁰Pb and ¹³⁷Cs measurements and applying the constant rate of supply (CRS) model. Major, trace, and radioactive elements were determined in surface samples and three sediment cores. Radioactive elements were determined by both alpha and gamma spectrometry. Major and trace elements were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using the EPA 3051a method. Enrichment factors (EF), contamination factors (CF), and pollution load indexes (PLI) were calculated in order to identify the human impact in both reservoirs, whereas the chemical index weathering (CIW) was used to assess differences in the degree of weathering.

Results and discussion

High uranium (U) enrichment (EFs?=?24.9–54.7) was observed in core layers at the San Marcos reservoir, while in surface sediments, this enrichment was lower. The high variability of lead (Pb) and As in sediment cores from the Granero reservoir was attributed to human influence. Arsenic and Pb enrichment differences between entry and exit sediment cores were explained by the filtering capabilities of the elongated shape, the topography, and the presence of plants on the reservoir’s bed. The highest PLI was found at the entrance core of the Granero reservoir.

Conclusions

The natural element concentration levels of As, Pb, and U were established at the Granero reservoir. High EFs for As and Pb suggest an anthropogenic origin of these pollutants at specific time intervals. High U concentrations in the San Marcos area are explained as naturally occurring. The concentrations of As in most of the studied sediments could pose a risk to human health by As ingestion, since they are above the probable effect level (PEL).

     

Thermal and water regime studied in a thin soil layer of green roof systems at early stage of pedogenesis

Purpose

The potential heat load and stormwater reduction of the anthropogenic, lightweight soil systems, such as green roofs, are valuable to heat island effect mitigation and to urban water management. Benefits of extensive green roofs, as widely used vegetated roof system with very thin soil layer, could be threatened by temporal changes of the soil structure.

Materials and methods

Green roof raised beds filled with two different anthropogenic soils (artificially constructed stripped topsoil with admixed crushed bricks and a commercial mixture of a technogenic substrate) were built to investigate the benefits of such systems in a temperate climate. These two soils were chosen with the intent to compare their thermal and water regime. One soil is expected to be favorable for hydrological functioning, whereas the other one for the thermal performance. Temperature and water balance measurements complemented with meteorological observations and knowledge of physical properties of the soil substrates provide the basis for detailed analysis of a thermal and hydrological regime in green roof raised beds. Moreover, the state of pedogenesis was studied on undisturbed soil samples by means of X-ray computed tomography.

Results and discussion

The water balance of green roof raised beds was calculated for a whole vegetation season and individual rainfall events. Runoff from raised beds was 38 and 63 % of received rainfall. On the basis of a detailed analysis of individual rainfall events, rainfall-runoff dependency was found for both raised beds. The difference between measured actual evapotranspiration and calculated potential evapotranspiration was discussed on the period with contrasting conditions in terms of moisture stress. Thermal characteristics of soil substrates result in a highly contrasting diurnal variation of soil temperatures. Analysis of X-ray computed tomography-derived macroporosity profiles reveals significant temporal changes in the soil comprised of the stripped topsoil with admixed crushed bricks.

Conclusions

Both green roof systems were able to reduce heat load of roof construction when comparing with the concrete roof construction. Similarly, received rainfall was significantly reduced. The extent of rainfall reduction mainly depends on soil, vegetation status, and experienced weather patterns. Methods used for non-invasive imaging proved to be beneficial for studying of soil structure changes.

     

Latent Process Modelling of Threshold Exceedances in Hourly Rainfall Series

Two features are often observed in analyses of both daily and hourly rainfall series. One is the tendency for the strength of temporal dependence to decrease when looking at the series above increasing thresholds. The other is the empirical evidence for rainfall extremes to approach independence at high enough levels. To account for these features, Bortot and Gaetan (Scand J Stat 41:606–621, 2014) focus on rainfall exceedances above a fixed high threshold and model their dynamics through a hierarchical approach that allows for changes in the temporal dependence properties when moving further into the right tail. It is found that this modelling procedure performs generally well in analyses of daily rainfalls, but has some inherent theoretical limitations that affect its goodness of fit in the context of hourly data. In order to overcome this drawback, we develop here a modification of the Bortot and Gaetan model derived from a copula-type technique. Application of both model versions to rainfall series recorded in Camborne, England, shows that they provide similar results when studying daily data, but in the analysis of hourly data the modified version is superior.     

Genetic variation of the durum wheat landrace Haurani from different agro-ecological regions

The durum wheat landrace Haurani (Triticum durum Desf.) is grown under contrasting climatic regions of Syria from Deir Ezzor, in the North-East (230 m altitude, 150 mm mean annual rainfall), to Qunaytra, in the South-West (1060 m altitude, 825 mm mean annual rainfall). In order to assess the genetic variation between and within Haurani populations, samples from eight provinces of Syria (Daraa, Damascus, Qunaytra, Deir Ezzor, Hassakeh, Aleppo, Homs and Hama) were analysed by RFLPs and seed storage proteins of glutenin subunits as markers. The analyses showed the presence of genetic polymorphisms in all populations with the highest values in those from Homs and Hassakeh. Moreover, the results point out differences in genetic distances between populations; some populations were further apart, such as Damascus and Aleppo, whereas others were closer to each other, for instance Homs and Hama. Cluster analysis identified two distinct groups of populations, characterized by geographical proximity, with similar rainfall and altitude. It is suggested that the similarity of landraces at locations close to each other might be the result of more frequent seed exchanges between farmers or of gene flow due to 5% estimated outcross rate of Haurani.