Dear Jan, that depends on your final goal - what do you want to obtain at the end: to get a biomass free of these metasls, or to use a biomass as the source of metals (i.e. to isolate metals). However in most cases the use of chelators is the best way to bind heavy metals. In most cases you can use a simle EDTA.

For most plant biomass, the method of Zheljazkov and Erickson (996) is the most straight forward. Tissues are milled with mortar and pestle. One g of milled plant matter is then soaked in 20 ml of concentrated nitric acid. After 6 h, the mixture is boiled to 50% of its original volume. Then, 4 ml of perchloric acid is added and the mixture ref- luxed for 90 min. The solution is then diluted with distilled water to 25 ml of total volume and analyzed with ̄ame atomic absorption spectroscopy. 

See any of my papers regarding heavy metals. There is information of the digestion procedures for all types of biomass and sediments.

Dear Jan, that depends on your final goal - what do you want to obtain at the end: to get a biomass free of these metasls, or to use a biomass as the source of metals (i.e. to isolate metals). However in most cases the use of chelators is the best way to bind heavy metals. In most cases you can use a simle EDTA.

Dear Jan,

the method described by Teresa Cutright is good. However, simple method as follow is also applicable:

Dry the biomass in the oven at 65 degree till a constant weight. Take about 0.5 g in 30 ml nitric acid (conc.) heat gently till the end of the brown fumes. Cool till room temp., add about 20 ml double distilled water and 5 ml hydrogen peroxide, heat very gently till the end of oxygen gas. Cool, transfer and dilute to 50 ml volumetric flask. use atomic absorption to detect the heavy metals.