Previous studies have shown that pteris vittata may accumulate substantial quantities of arsenic (As) in its shoots. The present study involved collecting soils from 21 contrasting sites from around England which had been contaminated with arsenic as result of a wide range of human activities and natural causes. These were used to examine growth and As uptake by P. vittata in a series of pot experiments. Initial experiments used soil from 10 fields on a large commercial sewage disposal estate located north east of Nottingham. These soils were highly organic and contained high concentrations of heavy metals (Zn, Cu, - Cd and Pb) but limited contamination with As. In some cases, the presence of high concentrations of heavy metals resulted in poor fern growth and limited removal of,As. With this information in mind, the remairjng 20 soils were collected from historically contaminated areas of England to provide a wide range of sources and severity of As contamination, a range of associated heavy metal concentrations and varying soil types. The results showed that the capacity of P. vittata to remove As from the soil may be severely limited by a range of influential factors in historically contaminated natural soils. Availability of the total As pool present was often very low, ranging between 1.7 and 16.9%. Indeed, soil solution concentrations were below the EU drinking water standard of 50 IJg L,l for all soils, with the Devon Great Consols humic soil having the highest solution As concentration of all soils examined, although this was nevertheless only 0.33 mg L-1 • This is believed to have occurred because the As was predominantly present as a constituent of minerals such as arsenopyrite in the mine spoil soils from the south west of England, or was strongly complexed within clay and iron oxides in the sewage treated soil. The highest percentage As removal was for two orchard soils (13.3 and 9.7%) in which the As present originated from pesticides containing chromated copper arsenate (CCA), a form of As known to be available to P. vittata, which had been applied over extended periods. The frequent co-occurrence of high concentrations of heavy metals in the study soils again adversely affected biomass production and As uptake by P. vittata. Factors such as low soil pH may also have reduced growth in some soils, as well as reducing the availability of As for uptake. High phosphate concentrations in some soils may have acted antagonistically to reduce As uptake, as demonstrated in an experiment in which phosphate Was added to three contrasting soils; low phosphate applications increased biomass and As uptake, whereas higher applications blocked As uptake. An uptake model was developed to predict the uptake of arsenic from field soils by P. vittata and facilitate assessment of the impact of a range of influential factors on the phytoremediation potential of this species. This model allowed the performance of P. vittata to be predicted under a variety of soil conditions and the time-frame required to remove the labile As pool to be estimated depending on whether this was replenished from other pools or not. The overall conclusions were that, although P. vittata may be unable to access and remove the extremely large non-labile pool of As in some soils, this species could provide a valuable tool for removing the labile and, hence potentially hazardous, fraction from contaminated soils.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:446147 |
| Date | January 2007 |
| Creators | Shelmerdine, Paula Ann |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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