Dominici Francesca, Peng Roger D, Ebisu Keita, Zeger Scott L, Samet Jonathan M, Bell Michelle L
Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21215, USA.
Environ Health Perspect. 2007 Dec;115(12):1701-3. doi: 10.1289/ehp.10737.
Lack of knowledge regarding particulate matter (PM) characteristics associated with toxicity is a crucial research gap. Short-term effects of PM can vary by location, possibly reflecting regional differences in mixtures. A report by Lippmann et al. [Lippmann et al., Environ Health Perspect 114:1662-1669 (2006)] analyzed mortality effect estimates from the National Morbidity, Mortality, and Air Pollution Study (NMMAPS) for 1987-1994. They found that average concentrations of nickel or vanadium in PM2.5 (PM with aerodynamic diameter < 2.5 microm) positively modified the lag-1 day association between PM10 and all-cause mortality.
We reestimated the relationship between county-specific lag-1 PM10 (PM with aerodynamic diameter < 10 microm) effects on mortality and county-specific nickel or vanadium PM2.5 average concentrations using 1987-2000 effect estimates. We explored whether such modification is sensitive to outliers.
We estimated long-term average county-level nickel and vanadium PM2.5 concentrations for 2000-2005 for 72 U.S. counties representing 69 communities. We fitted Bayesian hierarchical regression models to investigate whether county-specific short-term effects of PM10 on mortality are modified by long-term county-specific nickel or vanadium PM2.5 concentrations. We conducted sensitivity analyses by excluding individual communities and considering log-transformed data.
Our results were consistent with those of Lippmann et al. However, we found that when counties included in the NMMAPS New York community were excluded from the sensitivity analysis, the evidence of effect modification of nickel or vanadium on the short-term effects of PM10 mortality was much weaker and no longer statistically significant.
Our analysis does not contradict the hypothesis that nickel or vanadium may increase the risk of PM to human health, but it highlights the sensitivity of findings to particularly influential observations.
缺乏关于与毒性相关的颗粒物（PM）特征的知识是一个关键的研究空白。PM的短期影响可能因地点而异，这可能反映了混合物的区域差异。Lippmann等人的一份报告[Lippmann等人，《环境健康展望》114:1662 - 1669（2006年）]分析了1987 - 1994年国家发病率、死亡率和空气污染研究（NMMAPS）中的死亡率效应估计值。他们发现，PM2.5（空气动力学直径<2.5微米的颗粒物）中镍或钒的平均浓度正向修正了PM10与全因死亡率之间的滞后1天关联。
我们使用1987 - 2000年的效应估计值，重新估计了特定县的滞后1天PM10（空气动力学直径<10微米的颗粒物）对死亡率的影响与特定县的镍或钒PM2.5平均浓度之间的关系。我们探讨了这种修正对异常值是否敏感。
我们估计了代表69个社区的72个美国县在2000 - 2005年的长期平均县级镍和钒PM2.5浓度。我们拟合了贝叶斯分层回归模型，以研究特定县的PM10对死亡率的短期影响是否会被特定县的长期镍或钒PM2.5浓度所修正。我们通过排除个别社区并考虑对数转换数据进行了敏感性分析。
我们的结果与Lippmann等人的结果一致。然而，我们发现，当在敏感性分析中排除NMMAPS纽约社区中的县时，镍或钒对PM10死亡率短期影响的效应修正证据要弱得多，且不再具有统计学意义。
我们的分析并不与镍或钒可能增加PM对人类健康风险的假设相矛盾，但它突出了研究结果对特别有影响力的观测值的敏感性。
