Report No DWI0706

Jul 1987


This report describes studies made in conjunction with preparation of the booklet, "Methods for the Use of Plants to Monitor Heavy Metals in Freshwaters", in the series "Methods for the Examination of Waters and Associated Materials". The principle method in this booklet is the analysis of plant material to obtain information which complements or supplements that from chemical analysis of the water. Aspects which have been investigated include conditions for selection, preparation, drying and digestion of the materials and statistical treatment of the data.

Ten species are recommended for tissue analysis from U.K. waters: four algae (Lemanea fluviatilis, Cladophora glomerata, Enteromorpha flexuosa, Nitella flexilis), four bryophytes (Amblistegium riparium, Fontinalis antipyretica, Rhynchostegium riparioides, Scapania undulata) and two flowering plants (Elodea canadensis, Potamogeton pectinatus). Either the whole plant or a particular fraction of it is dried at 105º C. The results are presented of a series of tests on digestion techniques. These indicate that the concentrated and sometimes dangerous acid mixtures frequently reported in the literature are unnecessary. Nitric acid is recommended here, using 2 M for algae and bryophytes and 8 M for flowering plants .

The booklet deals in most detail with Zn, Cd and Pb, but also provides information for a number of other metals, especially Cr, Co, Ni, Cu and Ba. Comments on Hg are based on literature only, not our own research. A guide is given on how to make the most effective use of the analytical data. Datasets have been obtained (during previous surveys) relating metal concentrations (especially Zn, Cd and Pb) for six of these species to the concentrations found in their ambient environment. The possibility that regional differences might influence results was tested for Lemanea and Rhynchostegium. Where differences were found, these are probably due to overall differences in regional water chemistry. Bivariate and multlvariate equations based on these datasets permit those involved in pollution monitoring to make use of the known metal composition of a particular species to assess the metal composition of its environment during the period prior to sampling.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.