Species-specific tuning increases robustness to sampling bias in models of species distributions: An implementation with Maxent

Various methods exist to model a species’ niche and geographic distribution using environmental data for the study region and occurrence localities documenting the species’ presence (typically from museums and herbaria). In presence-only modelling, geographic sampling bias and small sample sizes represent challenges for many species. Overfitting to the bias and/or noise characteristic of such datasets can seriously compromise model generality and transferability, which are critical to many current applications - including studies of invasive species, the effects of climatic change, and niche evolution. Even when transferability is not necessary, applications to many areas, including conservation biology, macroecology, and zoonotic diseases, require models that are not overfit. We evaluated these issues using a maximum entropy approach (Maxent) for the shrew Cryptotis meridensis, which is endemic to the Cordillera de Mérida in Venezuela. To simulate strong sampling bias, we divided localities into two datasets: those from a portion of the species’ range that has seen high sampling effort (for model calibration) and those from other areas of the species’ range, where less sampling has occurred (for model evaluation). Before modelling, we assessed the climatic values of localities in the two datasets to determine whether any environmental bias accompanies the geographic bias. Then, to identify optimal levels of model complexity (and minimize overfitting), we made models and tuned model settings, comparing performance with that achieved using default settings. We randomly selected localities for model calibration (sets of 5, 10, 15, and 20 localities) and varied the level of model complexity considered (linear versus both linear and quadratic features) and two aspects of the strength of protection against overfitting (regularization). Environmental bias indeed corresponded to the geographic bias between datasets, with differences in median and observed range (minima and/or maxima) for some variables. Model performance varied greatly according to the level of regularization. Intermediate regularization consistently led to the best models, with decreased performance at low and generally at high regularization. Optimal levels of regularization differed between sample-size-dependent and sample-size-independent approaches, but both reached similar levels of maximal performance. In several cases, the optimal regularization value was different from (usually higher than) the default one. Models calibrated with both linear and quadratic features outperformed those made with just linear features. Results were remarkably consistent across the examined sample sizes. Models made with few and biased localities achieved high predictive ability when appropriate regularization was employed and optimal model complexity was identified. Species-specific tuning of model settings can have great benefits over the use of default settings.     

Validation of a HRGC–ECNI/LRMS method to monitor short-chain chlorinated paraffins in human plasma

Short-chain chlorinated paraffins(SCCPs) are produced in high volume and have the high potential to pose a threat to human health. However, little information is available for SCCP contamination in human blood/plasma/serum, mainly due to the difficulty of sample preparation and quantitative analysis. A method using high resolution gas chromatography coupled with electron capture negative ionization low resolution mass spectrometry(HRGC–ECNI/LRMS) was developed and validated to measure SCCPs in human plasma. The pretreatment process included protein denaturation and lipid elimination, liquid–liquid extraction with a mixture of n-hexane/dichloromethane(1:1, V/V), and cleanup on a multilayer silica column. The blank controls, including procedural blank, vacuum blood collection tube blank, and instrumental blank, were the most pivotal points for the reliable analysis of SCCPs. The average value of procedural blanks was 9.0 ng/g; and the method detection limit(MDL), calculated as the sum of the average procedural blank value and 3 times of the standard deviation of the procedural blanks, was 12.6 ng/g plasma. The validated method was applied to measure the concentrations of the total SCCPs(∑ SCCPs) in50 plasma samples from a general population. The measured plasma concentrations of ∑SCCPs ranged from MDL to 203 ng/g wet weight(ww), with an average value of 32.0 ng/g ww.The relative abundance profiles of SCCPs in plasma samples were dominated by C10- and C11-CP congener groups centered on Cl6–7. The developed method can be used for the comprehensive and large-scale investigation of SCCP levels in human plasma.     

Anaerobic digestion of sludge by different pretreatments: Changes of amino acids and microbial community

•Tryptophan protein, and aromatic protein I/II were the key identified proteins. •Cysteine was more correlated with methane production than other amino acids. •The presence of cysteine can promote methane production and degradation of VFAs. •The presence of cysteine can lower ORP and increase biomass activity. •Predominant Tissierella and Proteiniphilum were noted in pretreated sludge samples. Many studies have investigated the effects of different pretreatments on the performance of anaerobic digestion of sludge. However, the detailed changes of dissolved organic nitrogen, particularly the release behavior of proteins and the byproducts of protein hydrolysis-amino acids, are rarely known during anaerobic digestion of sludge by different pretreatments. Here we quantified the changes of three types of proteins and 17 types of amino acids in sludge samples solubilized by ultrasonic, thermal, and acid/alkaline pretreatments and their transformation during anaerobic digestion of sludge. Tryptophan protein, aromatic protein I, aromatic protein II, and cysteine were identified as the key dissolved organic nitrogen responsible for methane production during anaerobic digestion of sludge, regardless of the different pretreatment methods. Different from the depletion of other amino acids, cysteine was resistant to degradation after an incubation period of 30 days in all sludge samples. Meanwhile, the “cysteine and methionine metabolism (K00270)” was absent in all sludge samples by identifying 6755 Kyoto Encyclopedia of Genes and Genomes assignments of genes hits. Cysteine contributed to the generation of methane and the degradation of acetic, propionic, and n-butyric acids through decreasing oxidation-reduction potential and enhancing biomass activity. This study provided an alternative strategy to enhance anaerobic digestion of sludge through in situ production of cysteine.     

固定污染源NMHC-CEMS样品传输管线加热的必要性问题探究

针对非甲烷总烃在线监测系统（NMHC-CEMS）样品传输管线在不同伴热温度下对辛烷的吸附作用,以及管线自身的挥发情况开展研究。试验表明：在室温条件下,低、中、高质量浓度的辛烷标气在不锈钢传输管线中均有较为明显的吸附残留,在≥90 ℃的伴热条件下,辛烷在传输管内残留量对测定结果基本无影响,残留量明显低于1%,说明对样品进行加热传输是保证NMHC-CEMS测定结果准确性的必要措施。PTFE和PFA材质伴热管线在高温伴热下挥发明显,而不锈钢伴热管线更适用于NMHC-CEMS样品的传输。     

轻稳定同位素环境检测样品的采集和前处理方法

稳定同位素技术已被广泛应用于环境领域的鉴定、溯源、CN循环、反应机理等研究,检测样品的采集和前处理方法会直接影响研究结论。综述了目前在环境样品自然丰度的轻稳定同位素研究中,已被认可的样品采集和前处理方法的应用与进展,包括气体及其颗粒物样品、植物样品、沉积物样品、土壤样品、水样、生物样品和地质样品,为进一步提高数据的准确性、可靠性和多样性提供技术支持。     

Evaluating the blank contamination and recovery of sample pretreatment procedures for analyzing organophosphorus flame retardants in waters

Organophosphate esters (OPEs), used as flame retardants and plasticizers, are widely present in environmental waters. Development of accurate determination methods for trace OPEs in water is urgent for understanding the fate and risk of this class of emerging pollutants. However, the wide use of OPEs in experimental materials results in blank interference, which influences the accuracy of analytical results. In the present work, blank contamination and recovery of pretreatment procedures for analysis of OPEs in water samples were systematically examined for the first time. Blank contaminations were observed in filtration membranes, glass bottles, solid phase extraction cartridges, and nitrogen blowing instruments. These contaminations could be as high as 6.4–64 ng/L per treatment. Different kinds of membranes were compared in terms of contamination levels left after common glassware cleaning, and a special wash procedure was proposed to eliminate the contamination from membranes. Meanwhile, adsorption of highly hydrophobic OPEs on the inside wall of glass bottles was found to be 42.4%–86.1%, which was the primary cause of low recoveries and was significantly reduced by an additional washing step with acetonitrile. This work is expected to provide guidelines for the establishment of analysis methods for OPEs in aqueous samples.     

土壤样品中汞消解方法探讨

在使用ZYG—Ⅱ型智能冷原子荧光测汞仪测定土壤样品时,发现消解液中的盐酸试剂含有微量汞,使土壤中痕量汞的测定无法进行,本文采用巯基棉纤维提纯盐酸试剂并通过标准土样的测定对方法的准确度进行了验证。     

固相微萃取技术及其应用现状综述

固相微萃取技术（SPME）在固相萃取（SPE）基础上发展而来。作为一种较新的样品前处理技术,固相微萃取技术具有操作简单、快速、集采样、萃取、浓缩和进样于一体等诸多优点,目前已被广泛应用。阐述了 SPME 的技术原理、操作流程、影响因素、应用领域和新的进展。着重指出 SPME 在环境有机污染物分析中具有广泛的应用前景。     

浊点萃取在环境化学方面的应用

浊点萃取（ＣＰＥ）是一种新兴的液－液、液－固萃取方法，通过对该方法的相分离行为，改变实验参数如表面活性剂疏水性，平衡温度及时间、离心时间、ｐＨ值、离子强度、萃取物与表面活性剂浓度、添加剂等研究现状，综述了这一方面的原理、操作及其优化，并以ＰＡＨｓ等１７种有机污染物为例示，详细讨论了这一方法对环境样品的前处理技术，以及用于环境污染的进展，最后，探讨了该技术方法的发展前景。     

固相微量萃取技术

固相微量萃取（ＳＰＭＥ）法是一种新颖的样品处理方法。该文较详细地介绍了此法的原理、操作和应用等，并比较了此法与其它几种样品处理方法的优缺点。ＳＰＭＥ法的特点是简便、快速、灵敏、实用、经济、而且不会造成两次污染，有很好的发展前途。