短语讲解：

1.So far, they have collected almost 2,300 one-liter bottles of water from oceans and fresh waters all over the planet, even remote places.

so far 迄今为止; 到目前为止
例句：What have you found so far?
你到目前为止发现了什么？

2.They found, on average, fleece clothes lost .

on average 平均起来
例句：American shares rose, on average, by 38%
美国股票价格平均上涨了38%。

3.Patricia Holden explains the weight of these microfibers can add up.

add up 加起来; 总计
例句：The bills add up to exactly $100.
这些帐单加起来正好一百元。