Agriculture Reference
In-Depth Information
3.1 Baseline of PCDD/Fs concentration in soils
In the baseline survey (2007), PCDD/Fs concentration in this studied region is in the range
of 44.34 to 848.34 pg g
-1
(0.45 - 2.63 pg I-TEQ g
-1
) with a mean of 205.11 pg g
-1
(1.09 pg I-TEQ
g
-1
). It is lower than 4.0 pg I-TEQ g
-1
, which is PCDD/Fs limit standard for cultivation land
soil (GB15618-2009) in China (Ministry of Environment Protection, 2009), and this reflects
there is no remarkable PCDD/Fs contamination. The German guideline (Federal Ministry
for the Environment, 1992) recommends a limit of 5 pg I-TEQ g
-1
for unrestricted
agricultural use. US EPA (1998) recommends 1 pg I-TEQ g
-1
in residential soil and 5 pg I-
TEQ g
-1
in commercial soil. Zheng et al. (2008) did a review of PCDD/Fs source and level in
China, and found 0.09 to 2.4 pg I-TEQ g
-1
in mountain and 0.14 to 3.7 pg I-TEQ g
-1
in
farmland. According to the survey (Jou et al., 2007), it is observed that PCDD/Fs range from
0.10 to 8.48 pg I-TEQ g
-1
with an average of 2.20 pg I-TEQ g
-1
in soil collected from a nature
preserve area in Taiwan. Dioxin level in a urban surface soil in Norway is in the range of
0.16 to 14 pg I-TEQ g
-1
(Andersson & Ottesen, 2008), and PCDD/Fs baseline in rural soil in
Spain is 0.17 - 8.14 pg I-TEQ g
-1
(Schuhmacher et al., 2002). Therefore, PCDD/Fs level in this
survey is lower or generally comparative with the value of other places, beyond remarkable
pollution. Further, the highest concentration is in S2, which is obviously abnormal from
other sites. Actually, the surface and soil character in S2 is quite special, where is completely
bare without any plant or herb, the soil is like limestone, which is commonly used in
construction. So it is presumed that this point was polluted by some unknown historic
activity, especially during the MWI construction.
3.2 PCDD/Fs concentration and variation after MWI operation
After this MWI started operation, a significant variation of PCDD/Fs concentration in soil is
observed. In 2008, PCDD/Fs concentration ranges from 55.72 to 1981.89 pg g
-1
(0.53 - 5.78 pg
I-TEQ g
-1
) with an average value of 419.15 pg g
-1
(2.14 pg I-TEQ g
-1
). In 2009, PCDD/Fs level
is 66.82 - 1155.45 pg g
-1
(0.69 - 3.54 pg I-TEQ g
-1
) with an average of 277.73 pg g
-1
(1.70 pg I-
TEQ g
-1
). In 2010, PCDD/Fs level ranges from 85.01 to 1279.39 pg g
-1
(0.65 - 6.07 pg I-TEQ g
-
1
) with an average of 395.24 pg g
-1
(2.83 pg I-TEQ g
-1
). In the 2010 survey, the extraordinary
sample is S5, and the increase compared to the value in 2009 is up to 460.15 pg g
-1
(1.50 pg I-
TEQ g
-1
). So it is re-analyzed, and there is almost no difference between two measurements.
In the on-site place of S5, there is no obvious specific pollution source. S5 is located in a
hillside without herb or plants, and rain wash up is noticeable there. The possible
explanation is that pollutants on soil surface were washed by rain and enriched in S5.
Certainly, the persistent pollutant concentration in soil is the multi-result of pollution,
distribution, deposition and bio-degradation.
The overall variation of PCDD/Fs level in soil is shown in Fig.4 and Fig.5. Figure 4 is the
box plot of PCDD/Fs concentration each year, and Fig.5 is the comparison of PCDD/Fs
baseline and the average of PCDD/Fs level after MWI operation (2008 to 2010) in every
sites. In Fig.4, the PCDD/Fs variation is clear. PCDD/Fs level after operation is always
higher than the baseline, and there is a little drop in 2009 compared to 2008. As analyzed in
the previous paper (Li et al., 2010), the dioxin emission from this factory was largely
reduced because medical waste combustion decreased and a series of improvements
according to best available technique and best environment practice (BAT/BEP) were
implemented in August 2008 (Lu et al., 2008). After the improvement, PCDD/Fs
concentration in the stack gas and fly ash reduced by 96.7% and 83.15 %, respectively. This
is the major reason of the PCDD/Fs decrease in the 2009 survey. In Domingo's research
