Respiratory Health Division, National Institute for Occupational Safety and Health, Morgantown, West Virginia.
J Occup Environ Hyg. 2020 May;17(5):220-230. doi: 10.1080/15459624.2020.1734205. Epub 2020 Apr 10.
Fungi are ubiquitous in environments and produce secondary metabolites that are usually low-molecular-weight organic compounds during growth processes. Dust samples containing these fungal secondary metabolites collected from study sites are often stored in certain temperature conditions for an extended period until laboratory analysis resources are available. However, there is little information on how stable fungal secondary metabolites are over time at different storage temperatures. We examined the stability of 27 fungal secondary metabolites spiked into floor dust samples collected from a moisture-damaged office building. Ninety-five dust aliquots were made from the spiked dust; five replicates were randomly assigned to a baseline (time = 0) and each of the 18 combinations of three temperatures (room temperature, 4 °C, or -80 °C) and six time points (2, 12, 25, 56, 79, and 105 weeks). At the baseline and each subsequent time point, we extracted and analyzed the fungal secondary metabolites from the spiked dust using ultra-performance liquid chromatograph-tandem mass spectrometer. To estimate change in concentration over storage time at each temperature condition, we applied multiple linear regression models with interaction effect between storage temperature and duration. For 10 of the 27 fungal secondary metabolites, the effect of time was significantly (p-values <0.05) or marginally (p-values <0.1) modified by temperature, but not for the remaining 17 metabolites. Generally, for most fungal secondary metabolites, storage at room temperature was significantly (p-values <0.05) associated with a larger decline in concentration (up to 83% for 3-nitropropionic acid at about 11 months) than storing at 4 °C (up to 55% for emodin) or -80 °C (55% for asperglaucide). We did not observe significant differences between storage at 4 °C, or -80 °C. Storage temperature influenced degradation of fungal secondary metabolites more than storage time. Our study indicates that fungal secondary metabolites, including mycotoxins in floor dust, quickly degrade at room temperature. However, storing dust samples at 4 °C might be adequate given that storing them at -80 °C did not further reduce degradation of fungal secondary metabolites.
真菌在环境中无处不在，在生长过程中会产生通常是低分子量有机化合物的次生代谢物。从研究地点采集的含有这些真菌次生代谢物的灰尘样本通常在特定温度条件下储存很长时间，直到有实验室分析资源可用。然而，关于不同储存温度下真菌次生代谢物随时间的稳定性，信息很少。我们检查了从潮湿受损办公楼采集的地板灰尘样本中添加的 27 种真菌次生代谢物的稳定性。从添加的灰尘中制备了 95 个灰尘等分试样；将 5 个重复随机分配到基线（时间=0），并将 3 个温度（室温、4°C 或-80°C）和 6 个时间点（2、12、25、56、79 和 105 周）的 18 种组合中的每种组合的 5 个重复分配到基线和每个后续时间点，我们使用超高效液相色谱-串联质谱法从添加的灰尘中提取和分析真菌次生代谢物。为了估计在每种储存温度条件下随储存时间的浓度变化，我们应用了具有储存温度和持续时间之间相互作用效应的多元线性回归模型。对于 27 种真菌次生代谢物中的 10 种，时间的影响（p 值<0.05）或边缘（p 值<0.1）被温度显著（p 值<0.05）或边缘（p 值<0.1）修饰，但其余 17 种代谢物没有。一般来说，对于大多数真菌次生代谢物，在室温下储存（p 值<0.05）与浓度下降幅度更大（3-硝基丙酸约 11 个月下降 83%）相关，而在 4°C（大黄素下降 55%）或-80°C（asperglaucide 下降 55%）。我们没有观察到在 4°C 或-80°C 之间储存的显著差异。储存温度对真菌次生代谢物的降解影响大于储存时间。我们的研究表明，地板灰尘中的真菌次生代谢物，包括霉菌毒素，在室温下迅速降解。然而，考虑到将其储存在-80°C 并不会进一步减少真菌次生代谢物的降解，因此在 4°C 下储存灰尘样本可能就足够了。
