Aquatic macrophytes capture trace elements from water and store them in their tissues, which make them good biomonitors for these substances. But they also capture suspended particulate matter that could bias the concentration measurements in the moss tissues. To avoid this problem, many biomonitoring studies using mosses include a washing step in the sample preparation procedure.

However, no data is available on the quantities and variability of the particulate matter trapped by the moss, and the washing procedure has not been standardized between studies (washing time varied between 10 s to 30 min, divided in up to 7 washing steps). To study this, we extracted the particulate matter from samples of the moss Fontinalis antipyretica Hedw. collected in three rivers in NW Spain, washed them for 1, 2 and 5 min and collected the particulate matter extracted in each step. We also measured the contents of Al, As, Ba, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn in the tissues of the washed and unwashed mosses. We made a second experiment washing the samples only for 15 + 45, 30 + 30 and 45 + 15 s to determine if shorter washing times were adequate for cleaning the moss. In a third experiment we estimated the contents of particulate matter in moss samples collected monthly over a two-year period in two rivers in the same area.

The results showed that a) particulate matter can be as high as 40\% of the total weight of the sample, and that there were large variations within and between sampling sites, and over time. These results showed the need of washing the samples prior to their analysis; b) that two washings are needed for the removal of most of the particulate matter, but that 30 + 30 ∼ s are long enough to clean the moss, and c) that a 20:1 (or larger) water:moss relation is recommended to avoid saturation of the washing water, which would reduce the efficiency of the procedure.

We did not find significant losses of trace elements along the washing process, except for Cr in the three sampling sites, and Al, Fe and Pb in some of them. 1 min total washing time seemed the correct option both from the point of view of reducing the handling time of the samples and to prevent possible element losses.

水生大型植物从水中捕获微量元素并将其储存在其组织中，这使它们成为这些物质的良好生物监测器。但它们也捕获了悬浮颗粒物，这些颗粒物可能会使苔藓组织中的浓度测量产生偏差。为了避免这个问题，许多使用苔藓的生物监测研究在样品制备过程中包括洗涤步骤。

然而，没有关于苔藓捕获的颗粒物的数量和可变性的数据，并且研究之间的洗涤程序尚未标准化（洗涤时间在 10 秒到 30 分钟之间变化，分为多达 7 个洗涤步骤）。为了研究这一点，我们从苔藓Fontinalis antipyretica样品中提取了颗粒物质赫德。在西班牙西北部的三条河流中收集，洗涤 1、2 和 5 分钟，然后收集每一步提取的颗粒物。我们还测量了洗过和未洗过的苔藓组织中 Al、As、Ba、Cd、Cr、Cu、Fe、Hg、Mn、Ni、Pb 和 Zn 的含量。我们进行了第二个实验，仅将样品清洗 15 + 45、30 + 30 和 45 + 15 秒，以确定较短的清洗时间是否足以清洁苔藓。在第三个实验中，我们估计了两年内在同一地区的两条河流中每月收集的苔藓样品中的颗粒物含量。

结果表明，a) 颗粒物可高达样品总重量的 40%，并且采样点内部和采样点之间以及随着时间的推移存在较大差异。这些结果表明在分析之前需要清洗样品；b) 需要两次洗涤才能去除大部分颗粒物，但 30 + 30 ∼ s 的时间足以清洁苔藓，并且 c) 建议采用 20:1（或更大）的水:苔藓关系以避免洗涤水饱和，这会降低程序的效率。

除了三个采样点的 Cr 和其中一些采样点的 Al、Fe 和 Pb 外，我们没有发现在洗涤过程中微量元素有显着损失。从减少样品处理时间和防止可能的元素损失的角度来看，1 分钟的总洗涤时间似乎是正确的选择。