Cleaning and Stain Removal - How to remove 'stain/mold' of Bamboo Place-mat caused by rain-water

Hi:
Unintentionally, the five Bamboo Place-mats were left outdoor for few days and got blackish 'stain'/mold developed by rain-storm for the past weeks.

I tried to remove those ugly stain by diluted water with clorax and other good-quality cleaning solutions. Some of milder stain was removed by this, however there are still blackish and ugly stain on all corner of place-mats.

Is there any good clemical/cleaning solutions available to take off those ugly stain caused:confused: by rain-storm?

If there is/are no solution on cleaning, then is it possible to stain/pain those bomboo mats?

Thanks for your help in advance.

Natural fiber household accessories should not get wet. Because they are very absorbent, they quickly mold and mildew and tend to suffer from color loss and eventually disintegrate. Mold and mildew stains tend to be permanent. Why natural fiber household accessories are beautiful, they should not be used where they will likely get wet.