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III. Soil and Waste Composition Monitoring
CHEMICAL MONITORING OF SOILS
materials added directly or indirectly to agricultural land, the magnitude
of the chemical monitoring problem becomes self-evident.
Soil testing has developed on the premise that because of inherent and
man-induced differences in the availability of chemical elements to plants
grown on different soils, each field should be tested and treated separately
to eliminate deficiencies or toxicities of the elements most limiting to crop
production. A concerted effort among scientists will be required if this philosophy is to be extended to include all soil pollutants that adversely affect
crop quality and appear as toxic substances in the food chain.
Several approaches have been used in soil testing. Soils may be compared with respect to: ( a ) their total composition, (b) ion and compound
concentrations removed by strong extracting solutions, (c) ion and compound concentrations that reflect labile concentrations and activities withir.
the soil, and (d) biological assay results.
COMPOSITION OF SOILS AND
For soils and “agricultural chemicals,” defined above to include all materials applied to soils, obtaining a representative sample is a major problem. Segregation of particles has been a problem with commercial fertilizers. With waste products, such as sewage sludge, the composition
changes with time, the treatment process, and the method of sample preparation. Two-phase systems or suspensions with particles of nonuniform size
and specific gravity tend to produce nonuniform distributions and an absolutely representative sample may be impossible to obtain (Fair et al.,
1972). Sewage sludge samples vary in water content from a few percent
to 99%. Almost every type of sample presents a different problem in sample preparation and chemical analysis.
The method of sample digestion or extraction for macro- and trace elements will depend on how the element is bound, the temperature of vaporization and the method of analysis to be used. Principles of sample decomposition are discussed by Hawkes and Webb (1962). Digestion of samples
for total inorganic chemical composition may be accomplished using
Na,CO,, KHSO,, or NaOH fusion; H F and HC10, or H,SO, digestion;
NHOs and HCIO, digestion; or HNO, and H,O, digestion. As the organic
content increases, the fusion method becomes less dependable and oxidation with HNO, and HCIO, or H,O, becomes more effective.
Armstrong and Goldman ( 1969) noted that molybdenum is released
from organic materials by wet oxidation with HClO,, whereas the digestion
of silicate samples with H F givers higher recoveries than when HCIO, is
used and usually the recoveries are more reproducible than when fusion
DALE E. BAKER AND LEON CHESNIN
methods are employed. Meglen and Glaze (1973) recommend fusion with
potassium pyrosulfate (K2S,0i) for oxidation of sulfides. As an investigation on the recovery of trace elements in biological materials, the work
of Gorsuch (1959) is considered excellent. For routine analyzing of Se
and of less volatile elements including P, K, Ca, Mg, Mn, Fe, Al, Zn, Cu,
Ni, Mo, Cd, Pb, and Cr extracted from sewage sludge and plant material,
the HNO, and HClO, technique of Olson (1969) is used for routine analysis at the Pennsylvania State University. However, light scatter, molecular
absorption and other matrix interferences in flame emission, or atomic absorption analysis for some trace metals require the use of solvent extraction
(Dudas, 1974) and/or standard addition techniques.
A digestion procedure designed to completely remove one element may
remove only a fraction of the other elements. For the purpose of this discussion, a strong extractant is defined as a solution which when in contact
with soil or an agricultural chemical will render the material biologically
deficient with respect to the availability of the compound or ion being extracted. Thus, in addition to the extractions used to estimate total composition of soils and agricultural chemicals, other extracting procedures are
used. Kjeldahl method for nitrogen, hot 1 N HNO, soluble K and Mg and
1 N HCl soluble amounts of various elements have been used as a measure
of their supply in soils (LagerwerfT and Specht, 1970).
Peakall and Lincer ( 1970) reviewed analytical methods for PCBs
by means of a combination of high resolution gas chromatography and
mass spectrometry. Problems of differentiating PCBs from DDT and toxaphene have been discussed by Risenbrough et al. ( 1969).
The toxicity of elements varies inversely with natural abundance
(Schroeder, 1974). Therefore, teratogenic effects of trace metals on animals and man is expected to increase with a decrease in relative
abundance in the soil. Interpretation of results obtained from the use
of extractants to remove essentially all of a given element or compound
should be made with respect to its relative abundance in the soil or material
analyzed compared with its average content in soils or in the lithosphere.
For many organic soil pollutants, the additions have been made by man;
therefore, their biological persistence and effect within the food chain are
compared with a zero background level. For inorganic soil pollutants, including nonessential trace metals, all organisms have evolved in the presence of some background concentrations.
Some reported values have been summarized in Table VI for concentrations of elements in soils, the lithosphere, and some soil parent rocks.
Element Variations in Soils, the Lithosphere, and Rocks (in ppm of Dry Materialp
Swaine (1955); Rankama and Sahama (1968); Wedepohl(l970); and Hawkes and Webb (1962).
DALE E. BAKER AND LEON CHESNIN
Since the relationships between total soil composition and plant uptake
or an element are generally poor, the utility of values presented in Table
VI is up to question. Metals, which as a group are nondegradable in soils,
present a more complex and continuing problem than pesticides, PCBs,
SO,, CO, and other compounds that are degradable in soils. The total composition of soils and agricultural chemicals can be used to predict the relative changes in the food chain for an area. Any enrichment of soils with
rare metals like Cd will likely lead to accumulations within organs of animals and man (Doyle et al., 1974; Friberg et al., 1973; Schroeder and
Nason, 1974). Widespread enrichments of soils with some trace elements
could be detrimental to human and animal health.
The data in Table VI may be useful in predicting the probability of
significant changes in the food chain. If the compositions rank in the relative order of igneous rocks > shales > soil, then weathering processes can
be expected to decrease the biological activity of the element over time.
Elements in this group usually include Ca, Mg, S, Na, and for some will
include K, Fe, Mn, Zn, Cu, Cr, Co, F, Se, Hg, Li, and Pb. If the compositions rank in the relative order of igneous rocks < shales < soils, then
weathering will cause an increase in the biological activity of the element
over time. Such elements include P, Cd, Cr, V, As, Be, and for some
climatic areas Mo, B, Fe, and Mn. The presence of Zn and Cd in different
groups above might suggest that biological activity associated with soil
development leads to an enrichment with Cd compared with Zn.
Elements of the group whose activity is increased by weathering, including Cd, As, Be, and Mo, which are hazardous because of their adverse
effects on animals and man from long-term exposure to low concentrations, could be monitored and controlled in this manner until more precise
biological data are available for specific soils.
The labile concentration of an ion in soil is a measure of the. amount
of the ion which will reach equilibrium by isotopic dilution after a specified
time, usually 24 hours (Baker, 1964; Olsen and Dean, 1965).
The activity of an ion in soil water systems is analogous in concept to
ionic activity for solutions where the standard state is taken as a molal
solution of unit . activity. These parameters are related through Equation
where Ai is the activity or effective concentration of ion, i; 4; is the activity
coefficient for ion, i, in the system; and Ci is the labile concentration of ion, i,
These relationships for Mg and Cu have been described by Baker (1971,1972.
CHEMICAL MONITORING OF SOILS
1973). From Eq. (I), it is possible to compare the biological availability of
ions in soil-water systems to those in true solutions when conditions allow
certain assumptions to be valid:
1 . The labile quantity present and/or the dissolution rate of ion, i,
within the soil is sufficient to maintain a constant
over the plant uptake period under consideration;
2. The adsorption or ionic bonding properties of the soil do not change
during the plant uptake period.
3. The relative effect of other ions on the uptake of the ion under investigation does not change during the plant uptake period.
4. Other factors affecting rates of diffusion are not substantially different
for soils tested.
Except for soils very low in clay and organic matter, the labile concentrations of several elements in soils are sufficient to enable the assumptions
to be made for the purpose of soil monitoring of several elements (Baker,
1973 ) . Soil-plant relationships involving the concept and assumptions
above have been studied in relation to intensity factors, quantity or replenishment factors, relative intensity factors, and kinetic factors (Beckett,
1965, 1972; Oliver and Barber, 1966; Baker and Low, 1970; Barber,
1970, 1974; Khasawneh, 197 1) . Some soil-extracting solutions are useful
for indicating t i of Eq. ( 1 ) . If ion, i, is K, Ca, Mg, Na, Sr, Ba, Rb,
or Sc, then 1 N NH,OAc at pH 7 may be used following the procedure
of Chapman (1965). A high correlation exists for labile P in acid soils,
and Bray No. 1 P (0.025 N HCl, 0.03 N NH,F) using the procedure
by Olsen and Dean ( 1 965; Baker, 1964). For soils containing free calcium
carbonate, the Olsen method using 0.5 M NaHCO, at pH 8.5 is used as
a measure of for P. The procedure of Olsen and Dean (1965) has been
improved by use of the reagents proposed by Murphy and Riley (1962;
Watanabe and Olsen, 1965).
The use of 0.005 m diethylenetriaminepentaacetic acid (DTPA) at pH
7.3 removes a large part of the labile Fe, Mn, Zn, and Cu from soils high
in pH (Follett and Lindsay, 1971 ); and for acid soils (Lopez and Graham,
1972). Results of Hornick (1974) and Eshelman (1975) indicate that
DTPA in the range of 0.0016 M to 0.0062 M at pH 7.3 removes substantial amounts of Fe, Mn, Zn, and Cu from soils. For soils of medium to
high cation exchange capacity (CEC) , activities of several heavy metals
that reflect their availabilities may be estimated if the following are known:
( 1 ) the amounts extracted; (2) the equilibrium pH and the respective formation constants with DTPA when the DTPA concentration in solution
is no greater than 2 to 4 X lo4 M; (c) the soil to solution ratios which
are not greater than 1 : 10; and (d) the equilibration time, which is normally 24 hours (Council on Soil Testing and Plant Analysis, 1974).
Activity measurements for heavy metals in sewage sludge and other solid
BAKER AND LEON CHESNIN
wastes should be interpreted with great caution. The chemical forms may
change rapidly, and perhaps more important, the organic colloids will
greatly reduce the ionic activity coefficients from those in true solution.
However, as the organic colloids decay in soil these metals will be released
and their availabilities will be a function of their activity within the soil.
An excellent literature review, “Fate and Effects of Trace Elements in Sewage Sludge When Applied to Agricultural Lands,” has been prepared by
Page ( 1974).
Trace metals added to soils cause a permanent change in the soil
(Leeper, 1972) ;therefore, their additions to cropland soils should be based
upon their total concentrations in the soil. On the other hand, if land is
dedicated or permanently allocated for waste disposal and the production
of nonfood crops (see Chaney, 1973), then many concepts of soil science
relating to the effect of continued applications of organic matter and metalorganic complexes must be evaluated to maintain vegetation and prevent
water pollution via erosion and leaching. Soil reactions and properties
affected will include redox potentials, pH, microbial transformations, adsorption and soil physical parameters. The biological parameters of a program to keep the soil covered are complex but not insurmountable. The
sewage effluent and sludge disposal project at The Pennsylvania State University (Kardos and Sopper, 1973; Sopper and Kardos, 1973; Sopper,
1973) and the sludge disposal program of the Metropolitan Sanitary District of Greater Chicago (Hinesley et al., 1972; Hinsley and Jones, 1974;
Bauer, 1973; Barbolini, 1973) are examples of waste disposal on dedicated
In a review of techniques for studying the functions of soil biological
populations, Macura (1968) stated, “Methods are needed to study the
composite activities of microflora in the ecosystem, microflora-soil-plant,
and not merely the activities of individuals isolated from this system.” Respiration methods are most useful where a substrate is added to aerobic
soil and the rate of disappearance is compared with the synthesis of specific
enzymes. Several studies have been conducted on metal and organic pollutants in microbial degradation of sewage sludge I( Poon and Bhayahi, 1970;
Gunner, 1970; Bailey et al., 1970; Loveless and Painter, 1968; Swanwick
et al., 1968). Using a bioassay approach, Brown and Dalton (1970) were
able to predict the toxicity to rainbow trout of mixtures of Cu, phenol,
Zn, and Ni from the fractional toxicities of the particular poisons that were
present. Their results concerning additivity of metal toxicity lend some credence to the Zn equivalent factor calculated for sewage sludge by Chumbley (1971).
CHEMICAL MONITORING OF SOILS
Techniques similar to the Neubauer bioassay method (Vandecaveye,
1948) using wheat, barley, or oats as well as field beans or cucumbers
are useful in testing wastes for phytotoxic substances (Fryer and Evans,
1970). For samples of unknown origin, the effects of treating 100 g of
uncontaminated soil with 20,000-50,000 ppm of dry sewage sludge or other
waste material on the germination of oats and cucumbers is used at The
Pennsylvania State University in an effort to ensure that chemically undetermined phytotoxic substances (herbicides, etc.) are not present in materials to be applied to cropland. The bioassay techniques should be used
to prevent or minimize the frequency with which errors are made in the
field. The requirements of monitoring under field conditions cannot be
None of the existing bioassay techniques seem adequate for monitoring
pathogenic organisms including viruses (Bell, 1972), pollutants in the food
chains (Moriarty, 1972; Chaney, 1973), and especially ill-defined teratological effects of small doses of many trace elements (Underwood, 1971;
Davis, 1974) on animals and man.
Methods of Chemical Analysis
The chemical monitoring of soils and agricultural chemicals added to
them involves decisions on methods and frequency of sampling, the manner
of sample preservation and preparation, and the selection of methods of
analyses appropriate for the required accuracy of results. Difficulties experienced in obtaining a representative sample of soil or materials added to
soils does not decrease the requirements of precision and accuracy in sample preparation, digestion, or extraction and chemical analysis. Finally, a
critical evaluation must be made regarding the reliability, the statistical
significance, and ultimately the biological significance of the results. A biological significance should not be attributed to chemical analysis results
that are not statistically different because of variations resulting from sample collection, preservation, preparation, and/or chemical analysis. For example, the Cd signal by flame atomic absorption resulting from background
absorption by the Ca can often indicate erroneous positive results for Cd
in amounts up to 10 ppm.
When an upper limit for concentration of a material component is set
as in Table V, the stated value does not equal the desired upper limit in
composition to be tolerated. The true or desired upper limit plus the resultant sum of errors in sample collection, preservation, preparation and
chemical analysis are not expected to exceed the stated upper limit. A
stated upper limit of 50 ppm Cd in dry sewage sludge could represent a
desired upper limit of 25 ppm Cd plus 100% error or 33 pprn Cd plus
DALE E. BAKER AND LEON CHESNIN
50% error. From results for six sewage treatment plants of Pennsylvania
being sampled every 2 weeks, prepared and analyzed in duplicate, a 50%
coefficient of variation over time appears to be a realistic goal for a composite sample from a treatment plant.
In a discussion of the criteria for judging acceptability of analytical
methods, McFarren et al. (1970) point out that a method must be sufficiently precise (measured by coefficient of variation within one laboratory)
and sufficiently accurate (mean error from collaborative studies) if the
results are to be sensible and unbiased. Generally the results for trace elements are biased on the positive side especially when their concentrations
approach the detection limit of the procedure. The total error is defined
as the sum of two standard deviations plus the mean error expressed as
a percentage of the “true” value. Excellent methods have total errors of
25% or less; acceptable methods have total errors of 50% or less; and
unacceptable methods have total errors greater than 50%. McFarren et
al. (1970) concluded that atmic absorption spectrometry was acceptable
for the determination of Zn, Cr, Cu, Mg, Mn, Fe, and Ag but unacceptable
for the determination of Pb and Cd.
Adequate definitions of precision and accuracy are difficult (Murphy,
1961), especially when applied to an overall process or a “system of
causes” including the material, operator, instrument, laboratory and day.
Verification of the precision or accuracy is another measurement process
distinct from the one existing for the purpose of testing materials on a
routine basis. Chow et al. (1974) report a study in which prepared unlabeled samples of sea water were standardized for Pb at one university
by isotope dilution and circulated among participating oceanographic laboratories at seven United States universities and one in the United Kingdom. None of the laboratories obtained reliable values by either atomic
absorption or anodic stripping voltammetry.
Whitney and Risby (1975) suggested that methods of analysis should
be judged on the basis of seven factors: (1) required sensitivity, ( 2 ) accuracy of the method, (3) presence of interferences, (4) time per sample,
( 5 ) number and technical skill of laboratory personnel required, ( 6 ) required use of standard or reference methods, (7) cost per sample. Their review included 224 references providing an excellent summary of the current
status of optical, electrochemical, neutron activation, and chromatographic
methods. For optical methods, theoretical considerations are presented
for colorimetry, spectrophotometry, atomic fluorescence specrtrometry,
X-ray fluorescence spectrometry, and atomic absorption spectrometry.
Electrochemistry techniques are discussed for polarography, anodic strip-