Index System and Evaluation Method of Geological Environment Suitability for Human Health
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摘要:
人的健康与地质环境息息相关，地质环境对人群健康的影响一直以来备受环境、地质、医学等多学科领域研究者的关注。在环境健康影响评估方面，已有的研究注重从化学物质或工程建设等单一视角对健康风险进行评估，而从地球系统角度综合评估地质环境健康影响的研究尚不多见。本文提出从环境地球化学、区域地质背景、气候状况及人为活动强度等多维度出发，开展基于复合视角的地质环境健康适宜性评价指标体系与评价方法研究。本文建立了地质健康指数（GHI）评价方法，该方法按照GHI得分情况，将区域地质环境的健康适宜性分为优（85分及以上）、良（75~85）、一般（60~75）、较差（50~60）和差五个等级，分别代表区域地质环境处于极适宜、适宜、较适宜、可能适宜与不适宜人群健康的状况。本文以浙江省安吉与龙游两县为例，对GHI法的应用进行了案例分析。GHI法评价结果显示，两地在“气候状况”、“地质背景”与“人类活动强度”等三个分指数上得分相当，而在“环境地球化学”分指数上存在较大分异。这是因为安吉富硒土地农产品在富硒的同时重金属超标严重，而龙游富硒土地则无此类现象。两地GHI总指数得分显示，安吉地质环境的人群健康适宜性处于“良”级（78.16分），而龙游则处于“优”级（85.50分）。调查发现，两地居民健康状况差异不大，居民平均预期寿命均优于全国平均水平，说明虽然安吉地质环境存在高Cd、Ni的地球化学特征，但富硒环境起到了一定弥补作用，使得安吉整体上仍处于“适宜”人群健康的水平。GHI评价方法能够从总体上考虑与人群健康相关的地质环境要素，客观反映区域地质环境的健康适宜性状况，评价结果可以为合理利用有益健康的地质资源，以及规避不利健康的地质风险提供指导。
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关键词:
- 地质环境 /
- 人群健康 /
- 适宜性评价 /
- 地质健康指数（GHI） /
- 环境健康影响评估
Abstract:BACKGROUNDHuman health is closely related to the geological environment. There’re various geological environment factors affecting human health in a composite way. Geological background characteristics, including tectonic structure, lithologic features, and landform configuration shape the living conditions of human being. Climate conditions and the spatial and temporal variation characteristics influence the comfortable level for habitation. More importantly, the direct and indirect impacts of elements and chemicals in rock, soil, water, and air and biosphere on human health are comprehensive and significant. In addition, various human activities have increasingly influenced geological substances and geological processes since the Industrial Revolution, which together with natural geological factors contribute to the unique public health characteristics of a region. (Fig.1). Quantifying the impact of geological environment on human health has always been a hot topic in the study of environment, geology, and other disciplines. In terms of environmental health impact assessment, many scholars or organizations have developed different evaluation indicator systems from different research perspectives. Existing studies focus on assessing health risks from a single perspective, such as chemical substances or engineering construction, while comprehensive evaluation of the health impact of the geological environment from the perspective of the earth system is still rare. In today’s world of rapid socio-economic development, the relationship between human health and geological environment is even more complex, and single methods of evaluating environmental and population health are increasingly inadequate to cope with the increasingly complex health factors. The study of the suitability of geological environment for human health is rapidly progressing under a new theoretical framework.
RESULTS(1) The evaluation index system. A comprehensive geological environmental health suitability evaluation index system was developed based on a composite perspective, taking into account multiple dimensions such as environmental geochemistry, regional geological background, climate conditions, and intensity of human activities. The rock strata, topography, climate conditions, as well as the geochemical quality of multiple media such as soil, water, and crops in a certain area, shape the specific lifestyle and behavioral habits of the regional population, resulting in unique regional health characteristics. (2) GHI evaluation method. The geological health index (GHI) evaluation method was established, which divides the health suitability of regional geological environments into five grades based on GHI scores: excellent (85 points or above), good (75-85), fair (60-75), poor (50-60), and very poor, representing the conditions of extremely suitable, suitable, moderately suitable, possibly suitable, and unsuitable for human health. (3) Case study. A case study was conducted in Anji and Longyou counties of Zhejiang Province using the GHI method. The overall GHI scores of the two regions indicated that the health suitability of the geological environment in Anji county was rated as “good” (78.16), while Longyou county was rated as “excellent” (85.50). The evaluation results reflected the health suitability of the regional geological environment, and could provide guidance for rational utilization of geological resources beneficial to health and avoidance of geological risks adverse to health.
DISCUSSION(1) Principles for choosing indicators. The assessment index system was established following scientific principles, making sure the indicators are representative for general geological environment and closely related to human health. The influence of each indicator on health should be based on evidence, which can objectively reflect the difference of geological environment on population health. Furthermore, the indicators should be available in most settings and be simple to calculate. It is beneficial to have the current environmental industry or health industry standards as a reference. (2) Composition of the index system. The GHI index system included 15 specific indicators, which were listed in Table 1. Four sub-indexes were classified to represent the influencing factors of geological environment on human health, which were climate, geological background, environmental geochemistry characteristics and human activities. Two indicators of human comfort level, representing integrated influence of air temperature, humidity and wind, and incidence of extreme weather, were used to characterize the climate factors that affect human health. Four indicators, including regional crustal stability, natural environmental radioactivity, altitude and vegetation coverage, which were closely related to population health, were extracted to characterize the suitability of spatial characteristics of structure, rock, strata and epigenetic systems to population health. Seven indicators including environmental air quality, drinking water quality, irrigation water quality, cultivated land soil quality, agricultural product quality, water resource quantity and land resource quantity were used to characterize the environmental geochemical elements that have an important impact on population health. Human activities have influenced and changed the natural substances at global and regional scales, which have brought about significant impacts on the survival of organisms and human health. In this study, population density and per capita gross industrial and agricultural product were used to characterize the intensity of human activities. (3) GHI evaluation method. The evaluation of the health suitability of the geological environment was performed following the processes of data standardization, weight assignment, index score calculation and evaluation level classification. A two-step method was proposed to standardize data processing to complete the evaluation process of health suitability of the geological environment. Firstly, the environmental quality level corresponding to all indicators was determined by comparing with the national average level, national and industrial standards and specifications. Secondly, the impact of different levels of geological environmental quality on population health was evaluated with reference to literature, world and national health standards, and the degree of impact is measured with 0-100 points. The weights were assigned to each indicator according to analytic hierarchy procedure (AHP). The scores of each sub-index and total GHI index were calculated according to corresponding equation. Finally, the health suitability of regional geological environment is divided into five levels: excellent (85 points and above), good (75-85), general (60-75), poor (50-60) and bad (below 50), which respectively represent the state of extremely suitable, suitable, relatively suitable, possibly suitable and unsuitable to population health in certain regional geological environment. (4) Case study. A case study was conducted in Anji and Longyou counties of Zhejiang Province using the GHI method. The results showed that the two regions scored similarly in the three sub-indices of “climate conditions”, “geological background”, and “human activity intensity”, while there was a significant difference in the sub-index of “environmental geochemistry”. This was because the agricultural products in the selenium-enriched area of Anji were severely contaminated with heavy metals, while there was no such phenomenon in the selenium-enriched land of Longyou County. The overall GHI scores of the two regions indicated that the health suitability of the geological environment in Anji county was rated as “good” (78.16), while Longyou County was rated as “excellent” (85.50). However, the investigation found little difference in the health status of the residents in the two areas, with the average life expectancy of the residents in both areas higher than the national average. This suggests that although the geological environment in Anji County has high geochemical characteristics of Cd and Ni, the selenium-enriched environment has played a certain compensatory role, and Anji County still maintains an overall level of “suitable” for human health. (5) Limitations and future research prospects. With the rapid development of global society and economy, the relationship between population health and geological environment is complicated, and the evaluation method with single dimension is difficult to adapt to the increasingly complicated situation of health influencing factors. In this study, the GHI method is proposed to evaluate the health suitability of geological environment. Based on the multi-dimension of environmental geochemistry, regional geological background, climate condition and human activity intensity, the evaluation index system and evaluation method of geological environmental health suitability are studied from a composite perspective. The GHI evaluation method could be used for regional geological environment evaluation and zoning, and the evaluation results could help manage a more habitable environment and improve the health level of the population. However, there are still some limitations to this approach: ①There is no grouping of the target population. ②The exposure time is not considered. ③The actual intake of water and food is not confirmed. To sum up, the method will be continuously improved by refining the index system, to develop a health suitability assessment method with greater spatial heterogeneity that could meet the needs of the public and government to the greatest extent.
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天然气水合物，是在一定条件下(合适的温度、压力、气体饱和度及水的盐度等)由水和天然气组成的冰状笼形结晶化合物。形成天然气水合物的主要气体为甲烷，甲烷分子含量超过99%的天然气水合物通常称为甲烷水合物(Methane Hydrate)[1]。天然气水合物的结构类型有Ⅰ型、Ⅱ型、H型和一种新型的水合物(由生物分子和水分子生成)[2-3]。Kvenvolden等[4]和Milkov[5]曾预测全球有机碳超过1×105亿吨(甲烷在标准温压条件下为21×1015 m3)，主要以甲烷形式存在，并赋存于水合物中。目前，冻土带和海底已经开展了天然气水合物的相关实验及开采[6]。与冻土带所蕴藏的天然气水合物相比，海底沉积层中发育的水合物资源量可能更为巨大[7], 在全球79个国家累计已发现超过230个天然气水合物矿点(NGHD)[8]。因此，合理开采海底天然气水合物将是解决全球能源危机的有效途径[9-10]，同时天然气水合物也可能诱发海底地质灾害[11]以及影响全球气候的变化[12], 所以了解天然气水合物的稳定条件成了一个核心的科学问题。
甲烷水合物稳定性受控于温度、压力、孔隙水盐度和气体组分等因素。天然气水合物主要发育在具备水合物生成的温压、气源等条件的海洋沉积层中和极地地区[13-15]，所以研究水合物发育区的压力、温度、地温梯度、导热率及热流等参数，可以预测水合物赋存范围[16]。似反射层与海底之间所限定的厚度为天然气水合物稳定存在的厚度即天然气水合物稳定带(GHSZ)[17]。天然气水合物稳定带(GHSZ)是指温度和压力处于天然气水合物形成和稳定存在的热力学范围内的特定区域[18]。因而，预测目标区水合物资源量必须明确水合物稳定带厚度，对评估天然气水合物资源具有重要意义[19-21]。已有研究表明甲烷水合物实际存在区的厚度随盐度的增大而变薄，盐的存在降低了气体水合物的稳定性，导致水合物稳定带的厚度比纯水情况下的厚度变薄[22-23]。孔隙水中的盐类对水合物的生成和稳定存在有抑制作用[7, 24-25]，1888年Villard[26]第一次在CH4-H2O二元体系中获得了甲烷水合物。Deaton等[27]最早提出了研究水合物的抑制性，直到1983年de Roo等[28]才将盐度考虑进来，并系统研究了CH4-H2O-NaCl三元体系下甲烷水合物相平衡时的温压条件。事实上，盐度对水合物系统的影响是预测海底甲烷气水合物存在、分布和演变的一个重要因素。海相水合物形成于含海水(Cl-、Na+、Mg2+、SO42-、Ca2+以及过渡金属Fe、Mn、Cu、Co、Ni)的沉积层中，所以必须明确水合物在复杂体系中的平衡，拟为确定水合物的形成、分解以及资源量奠定基础[25, 29-30]。研究盐类对甲烷水合物的稳定性主要是通过实验测试(目测法、等压法、等容法)和热力学计算来确定天然气水合物的相平衡点[28, 31-37]。
1. 天然气水合物相平衡的研究方法
1.1 气体水合物相平衡热力学方法
气体水合物相平衡热力学主要解决气体水合物形成和稳定存在的温度、压力条件，预测已知状态系统是否可形成水合物，其理论依据主要是多相系统相平衡理论[34]。气体水合物相平衡的理论模型已经研究得比较成熟，并在指导水合物理论研究和工程应用方面发挥了积极的作用。Parrish等[38]第一次基于van der Waals-Platteeuw统计热力学模型[34]预测纯水条件下水合物的形成。随后这种方法被不断修改，但大多数预测模型的基本思想都来源于van der Waals-Platteeuw统计热力学模型[34]，预测模型的缺点就是所需的参数较多，计算繁琐，应用起来不方便[23-25, 30-32, 35-37, 39-41]。由于水合物形成于地层中，地层水是一个复杂的盐水体系，水合物形成的温度与纯水体系差异较大。Englezos等[42]、Shabani等[43]、Javanmardi等[44-45]的模型可用于预测盐水体系中水合物的相平衡。在盐水体系中，离子与水分子反应降低了水的活性，因此将盐对水合物的影响转移到水活性的变化，将溶液中水的活性加入到模型中来预测水合物相平衡。这些热力学模型计算水合物生成条件时，大多忽略了气体在富水相的溶解对水合物生成条件的影响，这会给计算结果带来一定的误差。水合物模型在适宜的温度(小于290 K)和压力(小于20 MPa)条件下的预测结果较好，而在高压下，如大于20 MPa，模型的预测结果与实验数据偏差较大，表明当前的水合物模型对于水合物稳定性描述并不完美[46]。
1.2 气体水合物相平衡实验分析方法
以往采用压力-温度-体积测试仪(简称PVT仪)来研究气体水合物的形成热力学，通过目测PVT仪中天然气水合物的形成过程，确定形成时的温度和压力，但是PVT仪器笨重且昂贵，不方便使用，实验过程中遇到固体微粒时，PVT方法就无法测量。此外，PVT无法定量评价天然气水合物的动力学性质[31]。后来将差示扫描量热仪(Differential Scanning Calorimetry，缩写DSC)应用到天然气水合物的研究中，它的原理主要是根据实验过程中热流量的变化判断水合物的形成，与样品的黏度、透明度等无关，是研究水合物一种简单、可靠的工具[47-48]。但是不能满足水合物的微观观测和定量研究。
相比于PVT仪、DSC、热力学计算，用原位拉曼光谱技术研究甲烷水合物生成条件可以有效地避免热力学方程中复杂参数的求算，同时具有可视、准确、结果可靠的优势。显微激光拉曼光谱是将入射激光通过显微镜聚焦到样品上，从而可以在不受周围物质干扰情况下，准确获得所照样品微区的有关化学成分、晶体结构、分子相互作用以及分子取向等各种拉曼光谱信息[49-50]。近些年来，国内外学者[51-56]已成功地应用激光拉曼光谱分析天然气水合物形成条件。Subramanian等[52]的研究表明，不同类型甲烷水合物的拉曼光谱明显不同，Ⅰ型甲烷水合物和Ⅱ型甲烷水合物的特征拉曼峰的峰强具有明显的差别，可以在拉曼谱图上明确区分开来(图 1)。Chazallon等[53]发现，甲烷水合物不仅在C—H键处有其独特的拉曼峰，同时其O—H键也有一个特征峰位于3051 cm-1。所以，通过拉曼光谱可以清楚地识别体系中甲烷所处的相态特征，这为原位甲烷水合物拉曼光谱分析提供了依据。吕万军等[56]通过原位拉曼光谱结合透明高压腔，测定甲烷水合物形成过程中溶液中饱和甲烷浓度的变化来确定水合物的形成条件。Jager等[33]结合显微拉曼光谱，可以将Ⅰ型甲烷水合物的形成和分解在拉曼谱图上清楚地确定，随着水合物的形成和分解，其拉曼峰也发生着相应的变化。因此，原位拉曼光谱技术可以准确测定甲烷水合物在不同盐水体系中形成和分解的温压条件。
2. 盐类对甲烷水合物的影响
根据DSDP(Deep Sea Drilling Project，深海钻探工程)和ODP(Offshore Driling Platform，海上钻井平台)[57]采集的海底沉积物，对孔隙水成分进行分析，结果表明海洋沉积孔隙水中，Cl-、SO42-、Na+、Ca2+、Mg2+、K+、NH4+是主要离子，CO32-和PO43-相对含量低一些。以下将从氯化物、硫酸盐、碳酸盐三大盐类出发，探讨盐类对甲烷水合物稳定性的影响以及相平衡条件。
2.1 氯化物对甲烷水合物稳定性的影响
2.1.1 氯化钠对甲烷水合物稳定性的影响
国内外学者[24, 28, 58-61]通过不同的实验研究了盐类，特别是NaCl对甲烷水合物稳定性的影响。对于NaCl-CH4-H2O体系，各种实验手段殊出同归，最后的实验数据皆表明随着NaCl浓度的增加，甲烷水合物稳定存在的温压范围逐渐缩小，NaCl浓度越高，甲烷水合物稳定存在的温度越低，压力越高。盐度每增加1 mol/L，在压力恒定的情况下，温度降低3~4 K；同样在温度恒定的情况下，压力升高2 MPa左右(图 2a)。除了NaCl，其他氯化物对甲烷水合物稳定性的影响也不容忽视，但整体的影响趋势是一致的，都是随着盐度的增加，甲烷水合物稳定存在的温压范围缩小[61-63]。
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2.1.2 其他氯化物对甲烷水合物稳定性的影响
目前针对CaCl2、MgCl2、KCl等对甲烷水合物的抑制作用研究甚少，Kharrat等[61]对不同浓度的CaCl2-CH4-H2O体系进行分析，随着CaCl2浓度的增加，甲烷水合物稳定存在的温压范围逐渐缩小，CaCl2浓度越高，甲烷水合物稳定存在的温度越低，压力越高。盐度每增加0.5 mol/L，在压力恒定的情况下，温度降低幅度由小变大最后趋于稳定，开始时温度只下降2.5 K，盐度在1.530 mol/L后温度稳定下降4 K左右；同样在温度恒定情况下，压力升高降低幅度由小变大最后趋于稳定，开始时压力只升高约2 MPa，盐度在1.530 mol/L后压力稳定升高约5 MPa(图 2b)。
Atik等[62]和Kang等[32]对不同浓度的MgCl2-CH4-H2O体系进行分析，随着MgCl2浓度的增加，甲烷水合物稳定存在的温压范围逐渐缩小，MgCl2浓度越高，甲烷水合物稳定存在的温度越低，压力越高。盐度每增加0.5 mol/L左右，在压力恒定的情况下，温度降低幅度由小变大；同样在温度恒定的情况下，压力升高幅度由小变大(图 2c，d)，即MgCl2盐度越高，对甲烷水合物的抑制作用强度越大。
Mohammadi等[63]对不同浓度的KCl-CH4-H2O体系进行分析，但是有关的实验数据较少，只对0.676 mol/L和1.315 mol/L的KCl进行了实验测试。随着KCl浓度的增加，甲烷水合物稳定存在的温压范围逐渐缩小，KCl浓度越高，甲烷水合物稳定存在的温度越低，压力越高。盐度每增加0.5 mol/L左右，在压力恒定的情况下，温度降低2 K；同样在温度恒定的情况下，压力升高1 MPa(图 2e)。
2.1.3 氯化物对甲烷水合物抑制作用大小
当氯化物浓度小于0.5 mol/L时，NaCl、CaCl2、MgCl2和KCl对甲烷水合物的抑制作用大小相近。但随着浓度的上升，当氯化物浓度大于1.5 mol/L后CaCl2对甲烷水合物稳定存在时的温压条件影响较大，浓度每升高0.5 mol/L，温度下降4 K，压力升高5 MPa。而其他盐类对甲烷水合物的抑制作用相近。浓度相近(大于1mol/L，小于1.5 mol/L)的NaCl、CaCl2、MgCl2和KCl对甲烷水合物的抑制作用进行对比，发现MgCl2对甲烷水合物的抑制作用最强，KCl最弱。抑制作用大小依次是MgCl2>CaCl2>NaCl>KCl(图 2f)。
2.2 硫酸盐和碳酸盐对甲烷水合物稳定性的影响
大部分的实验都是研究氯化物对甲烷水合物稳定性的影响，但是很少考虑到硫酸盐和碳酸盐对甲烷水合物的抑制作用，相关的研究也比较少。Lu等[65]通过实验确定了1 mol/L和0.5 mol/L的MgSO4对甲烷水合物稳定存在时的温压条件的影响，增加0.5 mol/L的MgSO4，在压力恒定的情况下，温度降低2 K；同样在温度恒定的情况下，压力升高0.7 MPa(图 3a)。相比于氯化物，MgSO4对甲烷水合物稳定存在时的压力影响较小。
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Mohammadi等[64]将K2CO3考虑进来，实验研究0.319 mol/L和1.064 mol/L的K2CO3对甲烷水合物的抑制作用，随着浓度的升高，甲烷水合物稳定存在的温压范围缩小，K2CO3浓度上升0.745 mol/L，在压力恒定的情况下，温度降低1.2 K；同样在温度恒定的情况下，压力升高1 MPa(图 3b)。相比于氯化物和MgSO4，K2CO3对甲烷水合物的影响更小。但是关于硫酸盐和碳酸盐对甲烷水合物抑制性的研究还较少，还不能明确硫酸盐和碳酸盐大类对甲烷水合物稳定性的影响，有待进一步的实验研究。
3. 盐类对甲烷水合物的抑制作用强弱
研究者们对不同盐类和不同离子对甲烷水合物的抑制作用大小进行了对比分析。何勇等[7]实验发现盐类对甲烷水合物的抑制作用大小为：NaCl>KCl>CaCl2>MgCl2>Na2SO4；Sylva等[24]的实验结果(图 4)与何勇等[7]的相近：FeCl3>NaCl>CaCl2≈AgNO3≈MnSO4>CuSO4≈FeSO4，可以看出NaCl是除了FeCl3外对甲烷水合物抑制作用最强的盐类。前人的系统研究结果与本文统计(基于Sylva等[24]、Mohammadi等[63-64]、Kang等[32]、Atik等[62]、Kharrat等[61]、de Roo等[28]、Maekawa等[59]、Lu等[60]的数据)的实验结果(即盐类浓度小于1.5 mol/L大于1 mol/L时，盐类对甲烷水合物的抑制作用大小为MgCl2>CaCl2>NaCl>KCl；盐类浓度大于1.5 mol/L时，CaCl2的抑制作用较强)存在较大的差异。可能由于统计的实验数据来自不同的实验测试方法，导致实验结果存在较大的差异。在阴阳离子对水合物稳定性的抑制作用大小上也出现了争议，有的认为Mg2+>Ca2+>Na+>K+，SO42->CO32->Cl-[66-67]，也有的认为Cl->SO42-，Mg2+≈Na+>Ca2+[60, 68-69]。实验结果差异较大，造成实验结果不一致的原因可能是在实验之前未完全将反应釜和溶液中的空气驱净，导致水合物合成受影响，也有可能是实验对比的盐类浓度上有差异，不同浓度的离子可能对甲烷水合物的抑制作用程度不一样。Lu等[60, 65]和Atik等[62]认为阴离子的存在对水合物稳定性的影响更大。在电解质溶液中，盐离子和水分子反应会降低水的活性，导致水合物不易形成[70-72]。理论上，阴离子半径越小、阳离子的半径越大和价位越高，对水分子的静电效应越强、溶剂效应和盐析效应越强，水的活性越低[73-74]。
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关于氯化物、硫酸盐和碳酸盐等抑制作用大小的比较，需要在同一实验测试条件下完成，但是前人并没有系统地研究其他盐类(如硫酸盐、碳酸盐等)对甲烷水合物稳定性的影响，未在不同盐类体系下针对甲烷水合物的稳定性进行横向和纵向的对比。关于盐类对甲烷水合物抑制作用的研究，已经从分子水平发展到离子水平。阴阳离子对甲烷水合物稳定性影响强度上存在较大的争议，阳离子如Mg2+、Na+、Ca2+、K+对甲烷水合物抑制作用大小的排序不统一，阴离子如SO42-、CO32-、Cl-对甲烷水合物的抑制作用大小争议更大。水的活性影响着甲烷水合物的形成，水的活性则受控于阴阳离子的半径电价等因素，因此探讨阴阳离子的性质对研究甲烷水合物在海水中的稳定性具有重要的意义。
4. 存在问题与展望
盐类对甲烷水合物的抑制作用是毋庸置疑的，但关于KCl、硫酸盐、碳酸盐等盐类对甲烷水合物影响的研究甚少，盐类对甲烷水合物的抑制作用大小存在差异，在不同盐类抑制作用强弱上也存在较大的争议。目前的研究结果还不够系统，与实际地质条件下的甲烷水合物稳定环境还存在一定差别。根据已有的研究成果，盐类对水合物稳定性影响的研究未来应关注以下几点。
(1) 以往的研究中对NaCl关注较多，关于NaCl对甲烷水合物的影响的研究已比较成熟，随着盐度的增加，NaCl对甲烷水合物的抑制作用越强，盐度每增加1 mol/L，在压力恒定的情况下，温度降低3~4 K；同样在温度恒定的情况下，压力升高2 MPa左右。但是地层水中还存在其他离子，如SO42-、CO32-、K+、Ca2+、Mg2+、NH4+，目前的研究成果与实际地质条件还存在一定差距，实际地层中的盐离子种类更多，更复杂，且不同的地质因素[如生物活动、水岩交互作用、深部物质(如甲烷气体)上流]会影响地层水盐度和离子种类的变化。因此，还需进行更加系统的研究，特别是要加强氯化物-甲烷-水、硫酸盐-甲烷-水、碳酸盐-甲烷-水等体系的详细研究。
(2) 本文数据统计结果显示，盐类浓度小于1.5 mol/L大于1 mol/L时，盐类对甲烷水合物的抑制作用大小为MgCl2>CaCl2>NaCl>KCl，盐类浓度大于1.5 mol/L时，CaCl2的抑制作用较强。盐类和离子对甲烷水合物的抑制作用大小和机制还需进一步确认，有待于系统地研究关于氯化物、硫酸盐、碳酸盐对甲烷水合物的抑制作用，并进行横向和纵向上的对比。同时阴阳离子对水合物稳定的影响强度还需进一步验证和分析，对比阴阳离子对甲烷水合物的稳定性影响的强弱，明确阳离子Mg2+、Na+、Ca2+、K+和阴离子SO42-、CO32-、Cl-对甲烷水合物的抑制作用大小，以及离子本身的性质如何影响着水的活性。明确盐类和阴阳离子的抑制作用大小，以及盐类和离子特性如何影响水合物的形成和稳定，对未来甲烷水合物的勘探和开发具有借鉴意义。
(3) 选取合适的实验手段，减小实验误差。将目测法、等容法、等压法三者相结合，目前实验手段中将高压可视反应腔与显微激光拉曼技术相结合可实现。这种实验手段能够在高压可视反应腔中清楚地观察到水合物的形成分解过程实现定性的研究，同时可根据拉曼谱图定量观测甲烷水合物的形成过程中液相中饱和甲烷浓度，准确获取甲烷水合物稳定形成时的温压条件。
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图 1 影响人群健康的地质环境要素系统
Figure 1. The conceptual linkage between human health and geological environmental factors. There ’re various geological environmental factors affecting human health in a composite way. Geological background characteristics, climate conditions, geochemistry behavior of elements and chemicals, as well as various human activities that have a profound impact on various geological processes, contribute jointly to an endemic public health status in a region.
表 1 地质环境健康适宜性评价指标体系组成与相应权重
Table 1 The evaluation indexes of geological suitability for human health and the corresponding weights.
总指数 分指数（权重） 指标（权重） 地质环境健康适宜性
（GHI）气候条件
（0.32）人体舒适度 （0.256） 极端天气发生率（0.064） 地质背景
（0.16）区域地壳稳定性（0.024） 天然环境放射性（0.040） 海拔高度（0.056） 植被覆盖率（0.040） 环境地球化学
（0.36）环境空气质量（0.108） 灌溉水质量（0.043） 饮用水质量（0.058） 耕地土壤质量（0.043） 农产品质量（0.050） 人均水资源量（0.029） 人均土地资源量（0.029） 人类活动强度
（0.16）人口密度（0.080） 人均工农业生产总值（0.080） 
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表 2 地质环境健康适宜性评价等级
Table 2 GHI scores and the corresponding human health suitability levels.
级别 指数 描述 优 GHI≥85 极适宜 良 75 ≤GHI<85 适宜 一般 60≤GHI<75 较适宜 较差 50≤GHI<60 可能适宜 差 GHI<50 不适宜
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表 3 GHI法在浙江安吉与龙游两地的应用
Table 3 Case study in Anji and Longyou by GHI assessment.
应用地区 基础评价 综合评价结果 气候状况 地质背景 环境地球化学质量 人类活动强度 总指数得分 浙江安吉 70 92.5 76.5 85 78.16 良 浙江龙游 70 92.5 96.4 85 85.50 优
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