Data Sheet 1_Effects of wetting events on mass timber surface microbial communities and VOC emissions: implications for building operation and occupant well-being.pdf

IntroductionHumans have used wood as a construction material throughout history. Currently, mass timber products, such as cross-laminated timber (CLT), are becoming more popular as a structural material, since they are renewable and have a lower carbon footprint than concrete or steel. Nonetheless, some building types, such as healthcare, veterinary, and food manufacturing, avoid using structural mass timber due to concerns about microbial growth in the event of wetting. One solution is to use protective coatings on mass timber products to increase moisture resistance, although the coatings themselves may generate concerns about volatile organic compound (VOC) emissions. Natural uncoated wood also produces VOCs, some of which may have intrinsic antimicrobial effects.
MethodsIn this study, we inoculated coated and uncoated cross- laminated timber (CLT) blocks with a mock microbial community and isolated each block within individual sealed microcosms. We characterized VOCs and surface microbial communities from the CLT blocks before, during, and after wetting periods of varying durations. VOC concentration and emission rate were analyzed with chromatography-mass spectrometry (GC-MS), while microbial community abundance, diversity, and composition were analyzed through qPCR and shotgun metagenomics.
ResultsVOC emissions were elevated immediately after inoculation, then decreased through the remainder of the experiment, except for a plateau during the wetting period. VOCs from uncoated CLT blocks were primarily terpenes, while coated blocks emitted VOCs associated with coatings, plastics, and industrial solvents, as well as terpenes. One VOC—acetoin (3-hydroxy, 2-butanone)—was present at high levels across all samples immediately after microbial inoculation. Bacteria comprised 99.54% of the identified microbial sequences. The plastic control microcosm (not containing a CLT block) had higher abundance of viable bacteria for the majority of the study, but there was no difference in abundance between coated and uncoated blocks. Prior to wetting periods, microbial composition was driven primarily by sampling day, whereas surface type played a larger role during and after wetting periods.

引言
古往今来，人类始终将木材作为建筑材料加以使用。当前，正交胶合木（cross-laminated timber, CLT）等重型木材产品作为结构材料愈发受到青睐，原因在于其具备可再生性，且相较于混凝土或钢材，碳足迹更低。然而，医疗、兽医诊疗及食品加工等部分建筑类型仍避免使用结构用重型木材，原因在于担忧受潮时会滋生微生物。对此，一种解决方案是在重型木材产品表面施加防护涂层以提升防潮性能，但涂层本身可能引发挥发性有机化合物（volatile organic compound, VOC）排放方面的安全顾虑。此外，未涂层的天然木材本身也会释放VOCs，其中部分VOCs还具备固有抗菌活性。

方法
本研究中，我们将模拟微生物群落接种至带涂层与未涂层的正交胶合木（CLT）试件中，并将每个试件单独置于密闭微型生态系统内进行培养。我们分别在不同时长的受潮周期前、中、后期，对CLT试件释放的VOCs以及表面微生物群落进行表征分析。采用气相色谱-质谱联用仪（GC-MS）分析VOC浓度与排放速率，通过实时定量聚合酶链式反应（qPCR）与鸟枪法宏基因组学分析微生物群落的丰度、多样性及组成结构。

结果
接种后VOC排放立即升高，随后在实验剩余阶段逐步下降，仅在受潮周期内维持平台期。未涂层CLT试件释放的VOCs以萜类化合物为主，而带涂层试件释放的VOCs除萜类化合物外，还包含与涂层、塑料及工业溶剂相关的成分。其中一种VOC——3-羟基-2-丁酮（acetoin）——在微生物接种后立即在所有样本中均呈现高浓度水平。在鉴定得到的微生物序列中，细菌占比达99.54%。在实验的大部分周期中，不含CLT试件的塑料对照微型生态系统内活菌丰度更高，但带涂层与未涂层试件之间的活菌丰度并无显著差异。在受潮周期开始前，微生物组成主要受采样日期影响；而在受潮期间及受潮后，试件表面类型对微生物组成的影响更为显著。