Laserfiche WebLink
i <br /> September 1996 -7- 963-2128.002 <br /> According to Soon and Bates (1982) NH4OAc extracts only exchangeable forms of Cu and <br /> Zn as well as other exchangeable trace metals. Based on personal communication with Dr. <br /> Robert Lerch, NH4OAc will displace all cations from the exchange sites and saturate the <br /> exchange sites with NH4+. Therefore, all exchangeable Cu would go into solution (Lerch <br /> 1996). <br /> Based on studies conducted by Singh, Singh and Rai, (1994) significant positive correlations <br /> were found between NH4OAc extraction and the Cu and Zn uptake by grasses. The amounts <br /> of Cu and Zn extracted by 1N NH4OAc (4.8) correlated significantly with Cu and Zn uptake <br /> by the two grasses. These investigators concluded that 1N NH4OAc (4.8) could be used for <br /> assessing the plant availability of Cu and Zn in metal polluted soils. <br /> 2.4 Correlation Between Extractability and Plant Availability of Trace Metals <br /> The plant availability of elements in soil is a function of their solubility and dissolution rate <br /> as they affect ionic activities in the soil suspension over time (ASA Mono. No. 9 1982b). <br /> The elemental concentration of plant tissue is influenced by the chemical composition of the <br /> growth medium, and is used frequently to appraise the nutritional status of plants and/or the <br /> fertility level of soil (Chapman 1966 and Tiller 1989). If the plant tissue concentration of a <br /> constituent that results in phytotoxicity can be determined, the critical concentration in the <br /> growth media and the permissible pollutant input can be calculated based on the rates of <br /> pollutant transfer from biosolids to soil and, subsequently, to the plant (Change et al. 1990). <br /> Selective chemical extraction is by far the most frequently used approach (Tisdall and Breslin <br /> 1995; Chang et al. 1984; and Singh, Singh, and Rai 1994) to sequentially remove trace <br /> metals in soils and biosolids. One of the major purposes in extracting trace metals with <br /> various reagents from composts is to estimate relative distribution of trace metals in various <br /> forms and consequently to identify which form(s) has high potential for plant uptake <br /> (bioavailability) and water contamination (Xin-Toa He, Taina, and Logan 1992). For <br /> L��vm�xua�ua,me noc Golder Associates <br />