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III. Soil and Waste Composition Monitoring

III. Soil and Waste Composition Monitoring

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CHEMICAL MONITORING OF SOILS



317



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.

A.



TOTAL

COMPOSITION OF SOILS AND

“AGRICULTURAL

CHEMICALS”



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



318



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).

B.



INTERPRETATION

OF TOTAL

COMPOSITION

RESULTS



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.



TABLE VI

Element Variations in Soils, the Lithosphere, and Rocks (in ppm of Dry Materialp

Rock composition



Soils

Element



P

S



Average

-



850



Fe

Al



Mn

Zn

cu

B



Mo

co

Ba

Cr

F

Se



V

As



Be

Bi

Cd

cs

Hg

Li

Ni



Pb



Sb



-



850

50

20.0

10.0

2.0

8.0

500



200

200

0.01

100

5.0

6.0

<1.0



0.5



5.0

0.03

30

40

10



-



Usual

range



400-3,000

100-1 ,500

14,OoO-40,

000



-



200-3,ooO

10-300

2-100

2-100

0.2-5.0

1-40

100-3,000

5-1 ,ooO

0.1-2.0

0.1-2.0

20-500

1-50



-



0.01-0.70

0.3-26

0.03-0.3

5-200

5-500

2-200



-



Lithosphere

average



-



Igneous



Limestone



1,300



900



40,600



90,ooo

1000



80

70.0

10.0

2.3

40



-



200



-



0.09

1 50

5.0

6.0

0.2

0.18

3.2

0.5

65

100



16



1 ,ooo



-



80

70

13

1.7



18

640



117

660

0.09

90

2.0-5.5

4.2

0.22

0.13

7.7

0.06

50

100

16

0.30



193

8,ooO

13,000

4,700

1,300

4-20

5-20

18

0.1-0.5

0.2-2

20-200

5

61

0.1-1.o

2-20



-






-



-



-



0.03

2-20

3-10

5-10



-



Swaine (1955); Rankama and Sahama (1968); Wedepohl(l970); and Hawkes and Webb (1962).



Sandstone



386

2,200

31 ,ooO

28,000

385

5-20

104



155

0.1-1.0

1-10

100-500



10-100

290

1 .o

10-60



-



<1

0.33



-



0.03-0.1

1-29

2-10

104

1 .o



Shale

817

1,100

43,000



0



90,400

-



z



50-300

30-150

130

1.0

10-50



E



p

r

O



2



300-600



g



100-400



2



590

0.5-1.0

50-300



v)



5.0



-



t;



0.3

13.2



0.4

50

20-100

20

3.0



”,

\o



320



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.



C. LABILE

CONCENTRATIONS

AND IONIC

ACTIVITIES

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

(1):



A,



=



Tic;



(1)



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



321



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



ci



322



DALE



E.



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

land.



D. BIOASSAY

TECHNIQUES

FOR CHEMICAL

MONITORING

OF SOILS

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



323



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

overemphasized.

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.

IV.



Methods of Chemical Analysis



A.



PRECISION

AND ACCURACY



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



324



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.

B.



INSTRUMENTAL

METHODS



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-



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