3 Micronutrient Elements (Fe, Mn, Cu, Zn) in Composted Solid Wastes and Composts-amended Soil

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Fig. 4.5. Water-soluble and total Ca in amended soil (81).



Fig. 4.6. Water-soluble and total Mg in amended soil (81).



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Fig. 4.7. Total contents of Fe, Mn, Cu, and Zn in various composts (81).



Total Fe, Mn, Cu, and Zn contents are mostly at much lower levels in both SPC (Fe:

593–1.17 × 103 , Mn: 106–129, Cu: 6.5–16, Zn: 63–82, mg/kg dry wt., respectively) and

GC (Fe: 923, Mn: 144, Cu: 4.2, and Zn: 19, mg/kg, respectively) than in other composts.

On the other side, Fe, Mn, Cu, and Zn are mostly high in SMC (Fe: 6.2 × 103 , Mn: 379,

Cu: 173, and Zn: 417, mg/kg, respectively), SMMC (Fe: 3.7 × 103 , Mn: 290, Cu: 142,

and Zn: 316, mg/kg, respectively), and SSC (Fe: 2.2 × 104 , Mn: 722, Cu: 345, Zn: 930,

mg/kg, respectively). As reported before (24, 25, 44, 60, 71), SMC and SSC are two of

the most widely concerned composts due to their high heavy metal contents. Nevertheless,

Cu and Zn contents in all these composts were below the USEPA “ceiling concentration”

for sewage sludge, that Cu should be no more than 4,300 mg/kg and Zn, 2,800 mg/kg (32).

Both Mn and Zn were found in large quantities in HEC (310–360 mg Mn/kg and 390–

590 mg Zn/kg), close to SMC and SMMC, while Fe and Cu were relatively lower. Moreover,

Mn was at high levels in CEC, next to SMC, SMMC, and HEC. Therefore, generally, such

an increasing order: SPC ≈ GC < HEC ≈ / < CEC ≈ / < SMMC ≈ SMC < SSC could be

concluded about total contents of Fe, Mn, Cu, and Zn in composted solid wastes.

Distributions of Fe, Mn, Cu, and Zn in various targeted composts are also presented in

Fig. 4.8. We can find the following: (1) The percentages of water-soluble and exchangeable Fe,

Mn, Cu, and Zn are significantly higher in SPC, GC, and HEC than in SMC, SMMC, CEC, and

SSC. (2) In all composts, Fe is predominant in organic matter-bound form. (3) Mn is mostly in

the carbonate-bound and Fe–Mn oxide-bound forms followed by the fractions associated with

organic matters-bound, water-soluble and exchangeable forms in SPC and GC; predominantly

in organic matter-bound form in SSC; mainly in Fe–Mn oxides-bound form followed by



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Fig. 4.8. Distribution of various chemical species of Fe, Mn, Cu, and Zn in various composts (81).



organic matter-bound, carbonate-bound, water-soluble, and exchangeable forms in SMC and

SMMC; mainly in the Fe–Mn oxides-bound and organic matter-bound forms in HEC; and

irregularly distributed in CEC. (4) The fractions of Cu in composts differ from that of Mn.

Water-soluble and exchangeable Cu in SPC, GC, and HEC mostly exceed 10%, and sometimes

as high as 40–50%, next only to the organic matter-bound form. Both water-soluble and

exchangeable Cu are at considerably high levels in SMC, SMMC, CEC, and SSC, but the

organic matter-bound forms of Cu are still in the majority (>80%). The degradation of organic

Cu compounds will result in the slow but continuous Cu release. (5) As for Zn distribution in

composts, Fe–Mn oxide-bound form is the main fraction. It is the most in SPC and GC, and

the second most in SMC, SMMC, CEC, HEC, and SSC (the most was organic matter bound

form). The carbonate-bound Zn counts more than exchangeable and water-soluble Zn in SPC,

GC, SMC, SMMC, and SSC, except for HEC, in which water-soluble Zn is found more.

2.3.2. Fe, Mn, Cu, and Zn in Composts-Amended Soils



The total Fe, Mn, Cu, and Zn contents of various soils are shown in Figs. 4.9–4.12,

respectively.

SPC applications led to the slight Fe and Mn decreases in soil, as can be contributed

partly to the lower level of Fe and Mn in SPC than in NSPS (Fe: 2.96 × 104 –3.41 × 104 ,

Mn: 288–587 mg/kg). Total contents of Cu and Zn in SPS-1 and SPS-2 also fell into the



Applications of Composted Solid Wastes for Farmland Amendment



Fig. 4.9. Total contents of Fe in amended soil (81).



Fig. 4.10. Total contents of Mn in amended soil (81).



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Fig. 4.11. Total contents of Cu in amended soil (81).



Fig. 4.12. Total contents of Zn in amended soil (81).



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narrow ranges (21–26 and 78–96 mg/kg, respectively), almost close to that of NSPS (25–

32 and about 85 mg/kg, respectively). Total element contents of GSs (i.e., GS, NGS, and

GSB) were all in the following ranges: Fe: 4.10 × 104 –6.25 × 104 ; Mn: 857–1.11 × 103 ;

Cu: 44–55 and Zn: 103–169 mg/kg, respectively. They were in agreement with the literature

values of uncontaminated soil: Fe: 4.0 × 104 ; Mn: 432; Cu: 2–250 and Zn: 10–300 mg/kg,

respectively (72–74). No significant Fe, Mn, Cu, and Zn accumulation has occurred. SMSs

(i.e., SMS, NSMS, and SMSB) and SSSs (i.e., SSS and SSSB) differed completely with SPSs

(i.e., SPS and NSPS) and GSs in the relationships among composts-amended soil, fertilizerused ones, and control soil. Slight decreases in total Fe and Mn contents of SMS-1 and

SMS-2 were observed due to the lower contents of elements Fe and Mn in SMC than in

SMSB (7.04 × 104 and 648 mg/kg, respectively). However, Fe and Mn contents of NSMS

(3.38 × 104 and 177 mg/kg, respectively) were lower even than that of SMSB. This is because

the land (NSMS) has been being used for rice production, and large amounts of Fe and Mn

were leached into groundwater. On the other hand, total Cu and Zn contents increased greatly

with compost uses. Unlikely, Fe and Mn, and Cu and Zn were at the same levels in NSMS

(13 and 78 mg/kg, respectively) as in SMSB (15 and 77 mg/kg, respectively) due to both the

lower solubility and the stronger organic-complex abilities of Cu and Zn than that of Fe and

Mn. As for SSS, the Mn, Cu, and Zn accumulations were very significant. Mn content in

SSS-1 and SSS-2 increased 2.7 and 2.9 times, Cu content did 4.8 and 9.0 times, Zn content

did 2.6 and 5.5 times, respectively, relative to SSSB (Mn: 84, Cu: 82, Zn 52 mg/kg), and Cu

contents even exceeded beyond the normal range of uncontaminated soil (WHO’s criteria, 2–

250 mg/kg). Conversely, the SSC addition caused Fe decrease in soil because Fe was at lower

level in SSC than in SSSB (2.86 × 104 mg/kg). The rainfall was also an important factor that

influenced the metal content in soil. It was found that Mn, Cu, and Zn contents in SSS-2, where

the farmland was covered with a plastic membrane to promote the maturity of semimature

composts, increased by 1.0, 1.7, and 1.8 times, respectively, relative to SSS-1, although SSS-1

has been amended for 6–7 years. These extra portions were attributed to water-soluble and

exchangeable metals, as well as those contained in tiny particles.

From Figs. 4.13 to 4.16, Fe, Mn, Cu, and Zn fractionations in various soils are shown,

respectively. No significant difference was observed for Fe, Mn, Cu, and Zn between SPS

and GS. The distributions in soil follow the order: organic matter-bound ≥Fe–Mn oxidesbound > carbonate-bound > exchangeable ≈ water-soluble. For SMC and SSC, all farmland

applications have lowered the percentages of the water-soluble and exchangeable Fe, Mn, Cu,

and Zn, while increased those of organic matter-bound elements in SMS, carbonate-bound,

and Fe–Mn oxides-bound forms in SSS. Although both water-soluble and exchangeable

elements are thought to be bioavailable, it is supposed that elements in other three forms (i.e.,

the organic matter-bound, carbonate-bound, and Fe–Mn oxides-bound) also be the “potential”

sources of available metals for plants (56), which might keep considerable concentrations of

elements in soil solutions.



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Fig. 4.13. Distribution of various chemical species of Fe in amended soil (81).



Fig. 4.14. Distribution of various chemical species of Mn in amended soil (81).



Applications of Composted Solid Wastes for Farmland Amendment



Fig. 4.15. Distribution of various chemical species of Cu in amended soil (81).



Fig. 4.16. Distribution of various chemical species of Zn in amended soil (81, 82).



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2.4. Heavy Metals (Cd, Cr, Ni, Co, Pb) in Composted Solid Wastes

and Composts-Amended Soil

2.4.1. Cd, Cr, Ni, Co, and Pb in Composted Solid Wastes



Experimental results (Fig. 4.17a) show that Cd has been found much more in SSC,

1.75 mg/kg, and in one special case of CEC, i.e., CEC-5, 1.85 mg/kg, than in SSB, 0.1–

0.4 mg/kg. Moreover, both HEC and SPC have rather high Cd concentrations (0.32–

0.46 mg/kg and 0.34–0.72 mg/kg, in HEC and SPC, respectively), close to that in SSB. Other

composts were popularly at low level, especially GC, Cd concentrations of them are all below

0.1 mg/kg. SSC should be considered to be one major Cd source to soils among solid waste

composts, and others are relatively small.



Fig. 4.17. Heavy metals in various composts (81).



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143



Cr has also been found significantly higher in SSC (63.7 mg/kg) than in other kinds of

composts (Fig. 4.17(b)). CEC also contains a considerable amount of Cr, and Cr contents

of CEC except CEC-1 are over 5 mg/kg. In GC and HEC, the composts with Cr contents

near 10 mg/kg also have been found. It is easily estimated that chemical impurities were

introduced into composted garbage, and that the uses of inorganic salts in chicken feeding

was an important cause for HEC. Apparently, large amounts of inorganic chemicals have been

found in these two HEC samples collected from two different regions in Yamaguchi Prefecture

of Japan. Low organic contents and surprisingly high solubility in strong inorganic acids, HCl

and HNO3 , may demonstrate this conclusion; and secondly, high level of water-soluble Cr has

been found and only less than organic matter-bound form. Data about Cr in both SMC and

SMMC are so few that here we cannot make a clear conclusion. Two SPC samples contain

much less Cr (0.28 and 0.13 mg/kg for SPC-1 and SPC-2, respectively), indicating at least

that seafood (fish and/or lobster), whose bones was used to produce SPC, is not the major Cr

accumulator. On the other side, although total contents are relatively low, considerable ratios

of water-soluble Cr have been found.

Figure 4.17c describes the existence of Ni in various composts. SSC contains a large

amount of Ni, 146 mg/kg, even exceeding the threshold level of Ni in soil in connection with

phytotoxicity, 100 mg/kg. About 70% of it is in organic matter-bound form, more than 20%

is in Fe–Mn oxides-bound form, and water-soluble form of nickel accounts for 3–4%. This

means that 1 kg of SSC contains nearly 5 g water-soluble nickel. GC-2 and two CEC samples,

CEC-2 and CEC-5, also have considerably high contents of Ni, but still lower than abovementioned threshold level of Ni. Contents of Ni in other composts are all lower than 10 mg/kg,

especially SPC.

SSC, like others (Fig. 4.17d), has a rather high content of Co, 18.55 mg/kg, higher than the

mean concentration in soil, 8 mg/kg, and lower than 40 mg/kg, the limit of phytotoxicity. This

level is not extremely safe for agricultural plants. All other composts have lower Co contents,

and the highest content was 2.25 mg/kg in one of GC samples. The application of composts

except for SSC cannot cause the Co accumulation in soil.

Different with other heavy metals in composts (Fig. 4.17(e)), the highest Lead content was

found in one of HEC samples, 49.65 mg/kg. The second highest is one of CEC samples, i.e.,

CEC-3, 21.30 mg/kg. However, they are still in the normal Pb range of environmental soil. In

other compost, Pb contents are all lower than 10 mg/kg.

2.4.2. Cd, Cr, Ni, Co, and Pb in Composts-Amended Soils



Figure 4.18 shows an extraordinarily high Cd content in the background soil, ranging from

24.7 to 34.6 mg/kg, far more than the literature value of background Cd. The Cd concentration

of SPC, 0.34–0.72 mg/kg, is about 1% of it. SPC applications have caused no significant Cd

increase in soil. Same with SPC, GC also contains little Cd, 0.08 mg/kg, and the accumulation

has hardly been caused in soil. SMC and SSC applications have caused significant changes

in Cd contents in soil. Cd contents of SMC are higher than the background Cd (about

0.037 mg/kg, which is much lower than that reported in literatures, 0.1–0.4 mg/kg) in testing

sites. Therefore, it is easy to understand that experimental results, SMS-1 > SMS-2 > SMSB.

At the same time, samples from fertilizer-applied soil also show an apparent increase in Cd