2022, Vol. 43
2016年10月25日, 中共中央、国务院发布的《“健康中国2030”规划纲要》中明确提出“共建共享、全民健康”是建设健康中国的战略主题.然而, 现如今建筑装饰材料和家居产品的广泛使用导致室内空气质量日渐恶化.挥发性有机化合物(volatile organic compounds, VOCs)作为主要的室内污染物, 其室内浓度比室外高出5倍[1].许多室内存在的VOCs与人体日常中的皮肤刺激、头痛、呼吸困难和哮喘甚至癌症有关, 甲醛和苯会加剧血液和呼吸道等问题[2~5].室内空气污染已然成为一个公共健康问题[6].
为了预防和控制室内环境污染, 保障公众健康, 我国制订了《民用建筑工程室内环境污染控制标准》(GB 50325-2020), 对污染物浓度限值进行了重新规定, Ⅰ类民用建筑中甲醛、苯、甲苯、二甲苯和总挥发性有机物(total volatile organic compounds, TVOC)的限值分别为0.07、0.06、0.15、0.20和0.45 mg·m-3, 该标准比《空气质量标准》(GB/T 18883-2002)中的限值要求更严格.因此, 迫切需要收集和报告新的住宅室内污染物浓度数据. Zhang等[7]的研究表明, 卧室中ρ(甲醛)和ρ(TVOC)的范围分别为0.06~0.10 mg·m-3和0.08~0.20 mg·m-3. Chang等[8]的研究发现卧室中甲醛和TVOC略高于客厅、厨房和浴室. Huang等[9]研究了西安市住宅污染物中甲醛癌症风险为5.73×10-5, 家具和建材贡献最大.国际癌症研究机构(IARC)将甲醛和苯列为第一类人类致癌物, 其在室内的污染也很普遍[10, 11].现已确定, 幼时暴露于环境污染物中的儿童患慢性病的风险会明显增加[12].然而, 目前对于污染物浓度水平及分布特征研究较多, 健康风险多是针对特定场所, 如加油站[13], 对于家庭环境中不同年龄段群体受到的健康风险研究较少.此外, 多种低浓度污染物叠加后的综合影响研究极为少见.
考虑到不同地区人居行为特征及环境条件的差异性, 本文以西北地区最大城市西安市居民住宅为研究对象, 通过实测住宅室内9种主要污染物(甲醛、苯、甲苯、二甲苯、TVOC、乙酸正丁酯、乙苯、苯乙烯和十一烷)浓度水平, 分析了季节变化对污染物浓度的影响和多种污染物叠加效应, 并评估了室内污染物对不同年龄群体的健康风险, 以期为进一步研究室内住宅污染物特征及其影响提供一定的科学依据.
1 材料与方法 1.1 样品的采集与分析本研究样品于2017年12月~2020年12月对西安市住宅小区共830户居民住宅室内污染物浓度进行监测, 其中包括卧室(1 254个)、客厅(1 072个)、书房(272个)和儿童房(461个)这4种房间类型.监测指标为甲醛、苯、甲苯、二甲苯、TVOC、乙酸正丁酯、乙苯、苯乙烯和十一烷这9种污染物, 并对小气候(温度、相对湿度)和装修时间等可能影响室内污染物浓度的因素进行了记录.
采样前, 所有监测房间至少关闭1 h以上, 采样期间门窗全部关闭, 以确保监测得到稳定的污染物浓度.甲醛采用气泡样管采样器(QC-2, 北京市劳动保护科学研究所)采集, 苯酚试剂分光光度法分析, 分析方法细节参考国家标准(GB/T 18204.26-2000); VOCs采用恒流采样器进行, 配有FID检测器的气相色谱仪分析(GC9790, 浙江福立分析仪器有限公司), 色谱条件参考国家标准(GB 50325-2001).取样装置安装在距地面高度约1.5 m处, 采样流量为0.5 L·min-1, 采样时间20 min.同时, 还测量了室外的对照样品和空白样品.
1.2 人体健康效应依据美国环境保护署(USEPA)健康风险评估模型[14], 参考环境保护部和中国环境暴露行为研究报告, 甲醛和苯的健康风险可通过下式计算：
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式中, CR表示致癌风险; I表示每日摄入量, mg·(kg·d)-1; CSF表示致癌斜率因子, kg·d·mg-1.其中甲醛为0.046 kg·d·mg-1, 苯为0.027 kg·d·mg-1
根据毒性效应的阈值机制[15], 苯、甲苯、乙苯和二甲苯的非致癌风险可通过下式计算：
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式中, HI表示风险指数; RfD为参考剂量; 根据综合风险信息系统(IRIS)提供的RfD值, 苯、甲苯、乙苯和二甲苯的参考剂量分别为0.0025、1.43、0.29和0.029 mg·(kg·d)-1, 其他相关参数列于表 1.
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式中, ci表示污染物浓度, mg·m-3; IR表示呼吸速率, m3·d-1; EF表示暴露频率, d·a-1; ED表示暴露持续时间, a; BW表示体重, kg; AT表示终身寿命, 25 550 d.
1.3 污染物叠加特性根据指数评价模型并参考室内空气品质评价方法[20], 采用加权平均值和沈晋明等[21]的方法计算室内多种污染物叠加指数P值, 其中：
加权平均值计算公式如下：
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文献[21]计算方式为：
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式中, P表示污染物叠加综合污染指数; Pi表示第i种污染物分项污染指数; Wi表示第i种污染物的权重. Ci表示第i种污染物的实测浓度, mg·m-3; Si表示第i种污染物的标准值, mg·m-3, n为污染物个数.各污染物分项污染指数和权重取值列于表 2.
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表 2 各污染物分项污染指数和权重取值 Table 2 Sub-pollution index and weight value of each pollutant |
经叠加后各污染物浓度值为：
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本次监测的西安市3 059个样本中室内污染物基本情况列于表 3, 污染物总体超标率高达30.7%, 主要污染物包括甲醛、苯、甲苯、二甲苯、TVOC、乙酸正丁酯、乙苯、苯乙烯和十一烷.其中, ρ(甲醛)主要分布在0.06~0.18 mg·m-3(图 1), 平均值为0.12 mg·m-3, 超标率高达92.1%.苯的最高超标倍数为8.23倍, 超标率为39.7%, 甲苯、二甲苯和TVOC的超标率分别为11.7%, 1.2%和8.9%.苯系物当中, 甲苯最为丰富, 约占40%, 其次为苯和二甲苯, 这与Du等[22]的研究结果一致.Chang等[23]研究了2014~2015年西安市住宅污染物情况, 甲醛超标率为83.6%(标准值0.10 mg·m-3), 未出现苯超标(标准值0.11 mg·m-3).本文所用的最新《民用建筑工程室内环境污染控制标准》(GB 50325-2020)中甲醛和苯的标准值分别为0.07 mg·m-3和0.06 mg·m-3, 污染物限值要求更加严苛, 故超标情况更严重, 超标率更高.
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表 3 西安市室内空气污染物检测结果 Table 3 Detection results of indoor air pollutants in Xi'an City |
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虚线位置对应标准值 图 1 不同污染物浓度下房间数量分布 Fig. 1 Room quantity distribution under different pollutant concentrations |
Pearson相关性检验表明(表 4), 各污染物浓度水平存在统计上的显著正相关(P＜0.01), 其中TVOC和苯系物之间的相关系数范围为0.614~0.747, 具有高度的统计显著相关性, 意味着它们具有相同或相似的来源.有研究表明, 住宅污染多来源于室内污染[25, 26].甲醛多来源于壁纸、粘合剂和胶合板等装饰材料; 苯及其同源化合物主要来自于家具漆、墙漆和各种内墙涂料[27, 28].正是由于人们多样化的需求导致房屋过度装修, 只注重美观性而忽视了环保性和健康性, 因而造成室内空气质量日趋变差.
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表 4 室内空气污染物Pearson相关系数1) Table 4 Pearson correlation coefficients of indoor air pollutants |
4种房间类型(卧室、客厅、书房和儿童房)中污染物浓度及超标情况列于表 5.卧室中污染物超标率相对最高, 客厅相对最低.卧室由于空间较小, 家具陈列较为密集, 且通常会依据个人喜好涂装各种墙壁图案, 放置家用纺织品、化妆品和其他药品[29], 因而超标较为严重; 与卧室相比, 客厅面积较大, 多以瓷砖铺地, 且长期开放, 通风情况更好[30, 31].总体来看, 不同房间类型中污染物浓度超标情况差异不大.Friedman检验结果表明, 卧室、客厅、书房和儿童房中甲醛浓度差异不显著(P＞0.05), 这与Dingle等[32]的研究结果一致.而苯、二甲苯和TVOC浓度具有统计学相关性(P＜0.05), 其中, 书房中苯系物平均值最高, 主要是各种书籍文件、打印机中油墨、颜料和合成材料等释放的污染物所致[33, 34].
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表 5 不同房间类型污染物浓度及超标情况 Table 5 Pollutant concentrations and standard exceedance in different rooms |
2.2 季节变化影响
考虑到季节变化对污染物的影响[35], 图 2展示了污染物浓度随季节变化的趋势为：夏季污染物浓度最高, 春秋两季浓度下降, 冬季部分污染物浓度略有回升.甲醛、苯和甲苯浓度冬季最低, 二甲苯和TVOC浓度秋季最低.其原因可能是西安冬季较为寒冷, 供暖期室内温度升高, 同时门窗长期关闭导致通风频率降低.Spearman秩相关分析表明绝大多数污染物与温湿度具有统计学相关性(P < 0.01), 温度与所监测的9种污染物均为正相关, 湿度与甲醛、苯和乙苯正相关, 与二甲苯、乙酸正丁酯、苯乙烯和十一烷负相关(表 6).其中, 甲醛受温度和湿度影响最敏感, 由于甲醛易溶于水, 相对湿度较大时胶黏剂中脲醛树脂水解, 从而释放甲醛; 而温度较高甲醛易从木质家具中蒸发, 不断向空气中扩散[36~38].本研究结果与相关报道一致[39, 40].表 7所示当温度高于25℃, 湿度超过60%时, 甲醛和苯的浓度更高, 其中温度对其贡献率分别为60%和67%.这可能是由于西安地处西北内陆地区, 全年气候干燥, 降雨量相对较少, 故湿度影响较小.
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图 2 不同季节各污染物浓度变化情况 Fig. 2 Variation in pollutant concentration in different seasons |
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表 6 温湿度与室内空气污染物Spearman相关系数1) Table 6 Spearman correlation coefficients between temperature and humidity and indoor air pollutants |
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表 7 温湿度对甲醛和苯综合效应的贡献率 Table 7 Contribution rate to combined effects of temperature and humidity on formaldehyde and benzene |
2.3 人体健康效应
甲醛、苯和乙苯已被世界卫生组织国际癌症研究机构列为致癌物质, 甲苯和二甲苯虽未被列为致癌物质, 但它们仍具有一定的致癌毒性, 对人体健康的影响不容忽视[41, 42].有研究表明, 家庭环境对总平均健康风险的贡献约为96%[43].在本研究中, 甲醛和苯的致癌风险范围分别为5×10-4~9.04×10-4和1.36×10-4~2.46×10-4(图 3), 均超过USEPA可接受的风险阈值(1×10-6), 且甲醛的致癌风险更高.不同年龄群体中, 儿童和老人对污染物的暴露更加敏感, 主要由于他们长时间呆在室内, 持续性暴露时间更长, 加之自身免疫力较低, 因而致癌风险更高.范洁等[44]研究了公共场所甲醛和苯的致癌风险范围分别为1.73×10-5~1.25×10-4和1.64×10-5~2.89×10-4, 可见室内致癌风险明显高于公共场所, 之前研究也获得相同结论[45].因此, 必须重视室内污染物对人体健康的不利影响.
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图 3 甲醛和苯的致癌风险评估 Fig. 3 Carcinogenic risk assessment of formaldehyde and benzene |
图 4绘制了苯、乙苯、甲苯和二甲苯的非致癌风险情况. 4种污染物的风险指数对不同年龄群体表现出一致性趋势, 即：老人＞儿童＞青少年＞成人, 这与大众的普遍认知相一致.苯的风险指数最高, 其次为二甲苯、乙苯和甲苯.其中, 苯具有明确的致癌风险(HI＞1), 其对成人的非致癌风险值已超过2, 致癌毒性必须引起重视.二甲苯、乙苯和甲苯处于低风险水平(HI＜1), 但它们对人体健康的有害影响依然值得重视.
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图 4 苯系物的非致癌风险评估 Fig. 4 Non-carcinogenic risk assessment of BTEX |
考虑到室内污染物以混合形式存在会产生一定的协同或拮抗效应, 尤其是前者会对人体健康造成更大的潜在威胁[46].污染物叠加前后超标变化情况显示(图 5), 加权平均值计算所得甲醛和苯的超标率分别增大至95.1%和51.4%; 沈氏模式得到甲苯和TVOC的超标率变为28.4%和25.6%.可以发现, 两种计算方式所得污染物超标情况不完全一致, 这是由于沈氏模式兼顾了最大单因子指数, 但未充分反映各污染物之间水平差异的信息, 故而其综合指数略大, 但两种方法均获得一致性结论, 即：污染物叠加之后毒性明显增强.室内污染物多以低浓度形式混合共存, 即使个体未超过标准阈值也并不意味着对人体无害, 尤其是多种污染物之间协同作用的发生导致毒性明显增大, 对人体造成更大的潜在威胁, 因此, 必须重视多重污染物的叠加影响.
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图 5 叠加前后污染物超标率 Fig. 5 Pollutant exceedance rate before and after superposition |
(1) 监测的9种污染物中甲醛污染最为严重, 超标率高达92.1%, 其次为苯、甲苯、TVOC和二甲苯, 超标率依次为39.7%、11.7%、8.9%和1.2%.甲醛浓度集中在0.06~0.18 mg·m-3, 平均浓度为0.12 mg·m-3. 4种房间类型污染物浓度总体水平及超标情况差异不大.
(2) 污染物随季节变化明显, 夏季污染物浓度最高, 甲醛、苯和甲苯浓度冬季最低, 二甲苯和TVOC秋季最低.温度与监测的9种污染物浓度水平均为正相关, 湿度与各污染物相关性正负不一, 其中甲醛受温、湿度影响最为敏感.
(3) 健康风险评估表明, 甲醛和苯对不同年龄群体(儿童、青少年、成人和老人)均存在致癌风险, 甲醛的致癌风险更高, 且儿童和老人受到的致癌风险更大.苯具有明确致癌风险(HI＞1), 二甲苯、乙苯和甲苯为低风险(HI＜1).
(4) 综合污染指数结果表明, 室内多种低浓度污染物之间存在叠加作用, 加权平均和沈氏模式两种方法均得到污染物超标率明显增大, 毒性作用大大增加, 因此必须重视多重污染物的协同效应.
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