Sociodemographic Characteristics of the E-waste Recyclers and Controls
The mean ± SD age of the e-waste recyclers and the controls assessed was 25.4 ± 6.3 and 32.3 ± 10.2 years, respectively. BMI was significantly higher in the controls (23.9 kg/m2) than e-waste recyclers (21.8 kg/m2) but was within a healthy body weight range for both groups (Supplementary Table 2). Majority of the e-waste recyclers (92%) and controls (84.3%) were Muslims (Table 1). More than half (55%) of e-waste recyclers were married, compared to (58.8%) of the controls who were single. Controls have had better education than e-waste recyclers; 41.3% of controls had completed Senior Secondary School, compared to just a third of the e-waste recyclers (32.3%) who reported to have completed Junior High School. Two thirds (63.6%) of e-waste recyclers earned between 20 and 100 Ghanaian cedis daily, and a 24.2% earned less than 20 Ghanaian cedis per day (~$4); and only 4% earned more than 200 Ghanaian cedis (~$35) per day. Furthermore, daily income earned was neither associated with educational status (χ2 = 4.42, p = 0.98) nor job task (χ2 = 6.73, p = 0.35) undertaken at the e-waste recycling site. More than half of the e-waste recyclers (55.2%) slept on-site, while the rest lived off-site either within 1 km of Agbogbloshie (36.5%) or more than 1 km away (8.3%). The recyclers reported to work approximately 9 hours per day for about 10 years. Finally, 36% of the e-waste recyclers were highly exposed to biomass burning than the controls (29%).
Table 1: Socio-demographic characteristics of e-waste recyclers and control group.
Demographics
|
Total
N
|
E-waste recyclers
n (%)
|
Controls
n (%)
|
χ2
|
p-value
|
Marital Status
|
150
|
|
|
4.43
|
0.06
|
Single
|
|
44 (44.4)
|
31 (60.8)
|
|
|
Married
|
|
55 (55.6)
|
20 (39.2)
|
|
|
Daily Income
|
149
|
|
|
5.12
|
0.16
|
<GHS 20
|
|
24 (24.2)
|
9 (18.0)
|
|
|
GHS 21-100
|
|
63 (63.6)
|
30 (60.0)
|
|
|
GHS 101-200
|
|
8 (8.1)
|
4 (8.0)
|
|
|
GHS >200
|
|
4(4.0)
|
7 (14.0)
|
|
|
Education
|
145
|
|
|
23.82
|
<0.01
|
None
|
|
25 (25.2)
|
6 (13.0)
|
|
|
Primary
|
|
26 (26.3)
|
4 (8.7)
|
|
|
Middle/JSS
|
|
32 (32.3)
|
12 (26.1)
|
|
|
Secondary/SSS & Higher
|
|
16 (16.2)
|
24 (52.3)
|
|
|
Religion
|
150
|
|
|
3.45
|
0.18
|
Muslim
|
|
92 (92.9)
|
43 (84.3)
|
|
|
Christian
|
|
5 (5.1)
|
7 (13.7)
|
|
|
Others
|
|
2 (2)
|
1 (2)
|
|
|
Smoking
|
146
|
27 (27.8)
|
6 (12.4)
|
4.52
|
0.03
|
Alcohol intake
|
151
|
17 (17.0)
|
9 (17.7)
|
0.01
|
0.92
|
E-waste Job-task
|
100
|
|
|
NA
|
NA
|
Burners
|
|
32 (32)
|
NA
|
|
|
Dismantlers
|
|
49 (49)
|
NA
|
|
|
Collectors/ Sorters
|
|
19 (19)
|
NA
|
|
|
Abbreviation: SD; Standard Deviation; NA: Not applicable
Dietary micronutrient intake (based on food models) of the -waste recyclers and the controls.
Dietary micronutrient intake is summarized in Table 2a. The dietary intake of Fe and Zn was significantly higher among the e-waste recyclers than controls, whereas Mg intake was higher among the controls (Table 2a). For other micronutrients (Ca, Se, Fe, Mg, Zn, Cu) assessed, there were no differences in consumption between e-waste recyclers and controls. For e-waste recyclers, the mean dietary intake of Ca, Se, Mg, Zn, and Cu was highest among those who were primarily involved in dismantling e-waste. In contrast, recyclers who were primarily involved in open-air burning of e-waste to retrieve valuable parts, especially Cu did not consume diets with adequate amounts of Ca, Zn, Cu and Fe. Overall, nearly all the e-waste recyclers (96%) and the controls (98%) met the RDA for Fe in this study. However, only a few of the e-waste recyclers (< 30%) met the RDA for Ca, Mg, Se, Zn and Cu (Supplementary Table).
Table 2a: Dietary micronutrient intake (based on food models) of e-waste recyclers and controls.
Dietary Micronutrient
|
|
E-waste Recyclers
|
Controls
|
|
intake (mg)
|
RDA (mg)
|
Mean±SD
|
Median (IQR)
|
Mean±SD
|
Median (IQR)
|
p-value
|
Ca
|
1000
|
534.4±352.3
|
449 (375.1)
|
557.0±369.6
|
497 (321)
|
0.47
|
Mg
|
350
|
45.7±44.2
|
33.3 (38.1)
|
84.7±67.3
|
59.6 (86.8)
|
<0.01
|
Se
|
55
|
22.8±18.0
|
17.9 (20.4)
|
32.2±39.9
|
19.8 (36.2)
|
0.50
|
Zn
|
11
|
11.3±4.1
|
10.6 (4.6)
|
9.7±4.7
|
8.7 (5.9)
|
0.01
|
Cu
|
2
|
1.1±0.6
|
1.0 (0.6)
|
1.0±0.7
|
1.1 (0.6)
|
0.12
|
Fe
|
8
|
26.5±13.0
|
24.2 (15.9)
|
22.4±10.5
|
24.8 (14.4)
|
0.04
|
Abbreviations: RDA-Recommended Daily Intake; SD: Standard deviation; IQR: Interquartile range. P-value estimate from the Wilcoxon rank sum test
Table 2b: Dietary micronutrient intake (based on food models) of key e-waste recycler groups. The groups were determined based on self-reported data, though recycler tend to perform a variety of tasks.
Dietary Micronutrient intake (mg)
|
RDA
(mg)
|
Burner
|
Dismantler
|
Collector/Sorter
|
p-value
|
Mean±SD
|
Median (IQR)
|
Mean±SD
|
Median (IQR)
|
Mean±SD
|
Median (IQR)
|
Ca
|
1000
|
453.3±164.8
|
418.3 (202.5)
|
582.8±439.1
|
468.5 (400.6)
|
546.3±321.5
|
534.5 (376)
|
0.67
|
Mg
|
350
|
46.1±38.4
|
39.9 (50.6)
|
49.7±52.5
|
34.3 (32.7)
|
34.1±24.7
|
26.9 (38.3)
|
0.48
|
Se
|
55
|
21.8±18.3
|
16.3 (21.4)
|
24.3±18.7
|
19.0 (18.1)
|
20.9±16.3
|
16.4 (24.6)
|
0.57
|
Zn
|
11
|
10.5±4.2
|
10.3 (5.7)
|
11.9±4.3
|
11.4 (5.1)
|
11.2±3.3
|
10.6 (4.3)
|
0.61
|
Cu
|
2
|
1.0±0.5
|
1.0 (0.7)
|
1.2±0.7
|
1.1 (0.6)
|
1.1±0.5
|
1.0 (0.8)
|
0.79
|
Fe
|
8
|
23.9±12.9
|
22.7 (13.3)
|
27.7±13.1
|
24.8 (14.4)
|
27.8±12.9
|
25.4 (18.6)
|
0.35
|
Abbreviations; SD: standard deviation; IQR: interquartile range; Ca: Calcium; Mg: Magnesium; Fe: Iron; Se: Selenium; Cu: Copper; Zn: Zinc. p-value estimate from the Kruskal wallis test
Micronutrient Biomarkers levels (Descriptive Summary)
In general, both the blood and urine datasets were deemed fit for analyses in terms of our review of quality control parameters. The average recovery (accuracy) of elements from the blood standard reference materials (SRM) used was 94% of the expected value for Se, Cu and Zn (Supplemental table 1). However, the mean analytical precision of all blood elements was 9%. In urine, the mean recovery
(accuracy) was between 63% and 123% for Cu, Zn and Se. Analytical precision for the urinary micronutrient measured was 15%. The accuracy of Ca, Fe and Mg in blood and urine could not be calculated as the reference materials used did not include guidance values for these.
For whole blood and urine samples analyzed, the mean concentrations obtained for Ca, Mg, Fe, Zn, Se, and Cu among the e-waste recyclers and the controls are reported in Table 3a. We further tabulated these biomarker values per job tasks performed (Table 3b).
Due to the unavailability of suitable biomarker reference levels for Ghana (or Africa), the mean micronutrient levels of Fe, Zn, Cu and Se in blood and urine were compared to values proposed by Iyengar and Woittiez (1988) in their effort to establish “normal values” for elements in biological samples. However, blood and urinary levels of Ca and Mg were compared to reference ranges established by Alimonti et al. (2005). In all, median levels of Ca, Zn and Se measured in whole blood of both e-waste recyclers and controls fell within these reference ranges. To ensure consistency, we also compared the urinary micronutrient levels with reference ranges established by Iyengar et al. (1988) and Alimonti et al. (2005). The estimated levels of the micronutrients in urine were within the normal range in both the e-waste recyclers and controls.
The median blood levels of Mg, Se, and Fe were significantly lower among the e-waste recyclers than controls (p < 0.05). Furthermore, among the e-waste recycler groups, median levels of Ca, Mg, Zn, and Se in blood were considerably highest among those who self-reported that they primarily collect/sort e-waste, followed by the dismantlers and then the burners. Significant differences were found in urinary levels of Ca, Se, and Fe among the e-waste recyclers and controls (p < 0.01). While urinary Ca and Se levels were higher among the controls, increased amounts of Cu were excreted among the e-waste recyclers (p < 0.01). Urinary Zn and Cu levels differed among the e-waste recycler groups (p <0.01). While Zn was particularly high in urine of the collectors/ sorters, Cu was highly removed in urine of the burners.
Table 3a: Micronutrient levels in blood and urine of e-waste recyclers and controls
Micronutrient Levels (µg/L)
|
Reference range
|
E-waste recyclers
|
Controls
|
p-value
|
Mean±SD
|
Median (IQR)
|
Mean±SD
|
Median (IQR)
|
Whole Blood
|
Ca
|
59028-72193
|
61992.1 ± 13610.6
|
63155.9 (16083.2)
|
65851.8 ± 9270.3
|
65629.4 (8835.7)
|
0.07
|
Mg
|
36951-43276
|
33717.2 ± 5694.1
|
34581.0 (6703.3)
|
38363.8 ± 4653.1
|
38560.7 (6481.2)
|
<0.01
|
Se
|
58-234
|
152.9 ± 39.8
|
145.9 (56.9)
|
194.9 ± 44.1
|
193.1 (49.4)
|
<0.01
|
Zn
|
4837-7980
|
7879.3 ± 2782.3
|
7242.9 (3267.6)
|
8355.2 ± 2466.9
|
8057.9 (2043.2)
|
0.09
|
Cu
|
683-1036
|
1107.9 ± 222.6
|
1110.9 (233.5)
|
1143.0 ± 234.1
|
1107.7 (259.6)
|
0.72
|
Fe
|
390000-550000
|
370697.2 ± 68181.2
|
381307.2 (77495.4)
|
404169.7 ± 65185.7
|
427274.6 (88040.3)
|
<0.01
|
Urine
|
Ca
|
67000-200000
|
66419.2 ± 75335.6
|
40243.9 (62094.9)
|
90814.3 ± 69028.3
|
71103.2 (96152.5)
|
<0.01
|
Mg
|
15000-120000
|
82220.5 ± 55215
|
71291.8 (72978.9)
|
82000.5 ± 56931.5
|
76954.6 (63733.0)
|
0.98
|
Se
|
7-160
|
29.7 ± 18.8
|
26.7 (22.3)
|
44.5 ± 25.8
|
39.9 (31.1)
|
<0.01
|
Zn
|
700-2500
|
3718.7 ± 7942.6
|
1044.4 (5022.0)
|
1561.8 ± 1294.2
|
1253.0 (1195.7)
|
0.89
|
Cu
|
12-80
|
63.7 ± 53.8
|
38.1 (76.6)
|
110.5 ± 567.8
|
25.6 (16.0)
|
<0.01
|
Fe
|
1.2-600
|
181.4 ± 351.8
|
95.4 (79.8)
|
114.4 ± 97.8
|
85.2 (52.3)
|
0.08
|
Abbreviations: Ca: Calcium; Mg: Magnesium; Fe: Iron; Se: Selenium; Cu: Copper; Zn: Zinc
Sources of reference ranges: Se, Fe, Zn, Cu -Iyengar and Woittiez (1988); whiles Ca and Mg were from-Alimonti et al. (2005) in blood and urine.
Table 3b: Micronutrient levels in blood and urine of e-waste recycler groups
Micronutrient levels (µg/L)
|
Reference range
|
Burner (n=32)
|
Dismantler(n=49)
|
Collector/Sorter(n=19)
|
p-value
|
Mean±SD
|
Median (IQR)
|
Mean±SD
|
Median (IQR)
|
Mean±SD
|
Median (IQR)
|
|
Whole Blood
|
Ca
|
59028-72,193
|
55577.0 ± 13646.0
|
55429.0 (18578.1)
|
62995.2 ± 11426.7
|
63719.6 (12923.5)
|
70209.5 ± 14240.9
|
68755.8 (11117.3)
|
<0.01
|
Mg
|
36951-43,276
|
30991.6 ± 6462.2
|
32633.0 (7851.5)
|
34903.6 ± 5403.7
|
35413.4 (6951.0)
|
35248.3 ± 5132.2
|
36003.3 (6693.6)
|
0.02
|
Se
|
58-234
|
135.1± 34.1
|
129.5 (33.8)
|
158.5 ± 41.8
|
159.7 (63.3)
|
168.6 ± 33.9
|
162.4 (51.5)
|
<0.01
|
Zn
|
4837-7980
|
6496.3 ± 2114.9
|
6667.9 (2356.9)
|
8105.2 ± 2594.0
|
7571.8 (2747.2)
|
9626.1 ± 3189.2
|
10069 (4126.8)
|
<0.01
|
Cu
|
683-1036
|
1038.4 ±249.3
|
1028.6 (324.4)
|
1126.5 ± 218.5
|
1107.8 (217.7)
|
1173.6 ±155.2
|
1131.6 (198.1)
|
0.12
|
Fe
|
390000-550000
|
350216.2±78098.1
|
368696.2 (120304.8)
|
382397.1 ± 58722.5
|
384963.9 (67423.7)
|
375166.5 ± 68887.8
|
389211.4 (75233.2)
|
0.19
|
Urine
|
Ca
|
67000-200000
|
61621.6 ± 73714.8
|
34674.6 (67557.2)
|
58091.7 ± 47212.3
|
53992.3 (60345.3)
|
95099.1 ± 120164.4
|
40548.7 (79110.5)
|
0.44
|
Mg
|
15000-120000
|
85002.8 ± 62528.2
|
66585.8 (81500.2)
|
78503.6 ± 53177.6
|
71412.0 (67174.9)
|
86729.0 ± 48965.0
|
86529.7 (59442.0)
|
0.70
|
Se
|
7-160
|
26.3 ± 20.2
|
20.7 (19.9)
|
32.3 ± 19.2
|
27.1 (22.9)
|
31.6 ± 15.1
|
32.3 (23.3)
|
0.15
|
Zn
|
700-2500
|
1548.1 ± 2012.8
|
784.5 (769.1)
|
5368.0 ± 11138.6
|
1047.6 (5022)
|
3468.2 ± 2729.4
|
4597.4 (5473.2)
|
<0.01
|
Cu
|
12-80
|
87.7 ± 57.6
|
97.6 (87.3)
|
48.3 ± 57.6
|
87.3 (82.6)
|
61.2 ± 64.8
|
33.8 (43.0)
|
<0.01
|
Fe
|
1.2-600
|
108.9 ± 69.4
|
87.3 (82.6)
|
108.9 ± 69.4
|
100.4 (68.9)
|
426.5 ± 744.7
|
100.4 (153.6)
|
0.19
|
Abbreviation: SD: Standard deviation; IQR: Interquartile range; Ca: Calcium; Mg: Magnesium; Fe: Iron; Se: Selenium; Cu: Copper; Zn:
Sources of reference ranges: Se, Fe, Zn, Cu -Iyengar and Woittiez (1988); whiles Ca and Mg were from-Alimonti et al. (2005) in blood and urine.
Relationship between dietary micronutrient intake and micronutrient levels in the blood and urine of e-waste recyclers
The correlations between dietary micronutrient intake and levels of micronutrient in the blood and urine of e-waste recyclers are presented in Table 4. Between dietary intake values and blood levels, few of these relationships were significantly positive (5 out of 36; Mg-Fe, Ca-Zn, Mg-Zn, Mg-Se and Mg-Mg), whereas for urine only one associated was significantly positive (Mg-Cu) and ~50% of them were negative.
Table 4: Correlation coefficients between dietary (D) micronutrient intake (top row) and micronutrient levels in blood (B) and urine (U) of e-waste recyclers (first column). Bolded numbers indicate correlations that are of statistical significance.
Biomarkers (µg/L)
|
D-Ca (mg)
|
D-Mg (mg)
|
D-Fe (mg)
|
D-Se (mcg)
|
D-Cu (mg)
|
D-Zn (mg)
|
B-Ca
|
0.15
|
0.17
|
0.06
|
0.11
|
-0.04
|
-0.002
|
B-Mg
|
0.11
|
0.27**
|
0.04
|
0.09
|
-0.03
|
0.002
|
B-Fe
|
0.17
|
0.17*
|
0.10
|
0.10
|
0.001
|
0.06
|
B-Cu
|
-0.02
|
0.17
|
0.04
|
0.02
|
-0.04
|
0.001
|
B-Zn
|
0.29**
|
0.18*
|
0.11
|
0.13
|
-0.03
|
0.08
|
B-Se
|
0.16
|
0.21*
|
0.07
|
0.07
|
-0.06
|
0.002
|
U-Ca
|
0.04
|
-0.09
|
-0.06
|
0.07
|
0.21**
|
-0.10
|
U-Mg
|
-0.003
|
-0.10
|
-0.07
|
0.03
|
-0.06
|
-0.10
|
U-Fe
|
0.11
|
-0.04
|
0.07
|
0.01
|
-0.02
|
0.09
|
U-Cu
|
-0.05
|
-0.21**
|
-0.09
|
0.05
|
0.09
|
-0.11
|
U-Zn
|
0.07
|
0.09
|
0.02
|
0.12
|
-0.04
|
-0.01
|
U-Se
|
0.06
|
-0.11
|
-0.12
|
0.12
|
0.01
|
-0.09
|
Abbreviations: D-Dietary; U-Urinary; B-Blood
p-value notation: *p<0.05, **p<0.01
Association of sociodemographic characteristics and other work-related factors with dietary micronutrient intake among e-waste recyclers
We further evaluated micronutrient-intake associations with daily work duration, age, daily income earned, educational status, exposure to biomass burning, cigarette smoking, alcohol intake, BMI and recycler job task (Supplementary Table 4a). Factors such as hours spent recycling e-waste and daily income earned were associated with dietary Ca and Fe consumption. BMI was also positively associated with the consumption of foods rich in Mg, Cu and Se. On the other hand, educational status was inversely associated with dietary Mg intake (β = -0.19; 95% CI: -0.36, -0.02, p = 0.03). Most factors, such as age, job task undertaken, cigarette smoking, exposure to biomass burning and alcohol intake, were not associated with the dietary intake of micronutrient-rich diets.
Relationships between selected work-related factors and blood and urinary micronutrient levels
Exposure to biomass burning was associated with the lower levels of Mg, Zn and Fe measured in the blood of e-waste recyclers (Supplementary Table 4b). Moreover, increased duration of work at the recycling site was inversely proportional to Mg levels in the blood of e-waste recyclers. The nature of e-waste job-task performed significantly influenced blood levels of Ca, Mg, Zn and Cu, with collectors/ sorters having the highest. However, factors such as daily work duration, age, BMI, cigarette smoking and alcohol intake did not influence the blood micronutrient levels.
We also investigated the associations between job-related factors with urinary micronutrient excretion (Supplementary Table 4c). Significant relationships were found between years of recycling e-waste and urinary levels of Ca (β = 0.08; 95% CI: -0.01, 0.15, p = 0.02) and Cu (β = 0.09; 95% CI: 0.04, 0.13, p = 0.004). Furthermore, we found that cigarette smoking was associated with lower levels of Ca, Mg, and Zn excreted in urine of e-waste recyclers. Urinary levels of Cu were also lower with increasing age (β = -0.07; 95% CI: -0.11, 0.03, p = 0.004). Meanwhile, exposure to biomass burning as well as factors such as alcohol intake, BMI, job task undertaken and the number of hours (per day) spent recycling e-waste did not have any significant influence on urinary levels of the micronutrients measured.