Table 2.

Bivariate associations of manganese (Mn) concentrations (μg/g) with characteristics of farmworkers, Zarcero County, Costa Rica, 2016.

	Toenail Mn (n = 40)^a		Hair Mn (n = 33)^b
Characteristics	GM (GSD)	p-value^c	GM (GSD)	p-value^c
All	0.40 (3.52)		0.24 (3.54)
Age^d		0.02		0.64
18–29	0.76 (3.07)		0.21 (4.32)
30–49	0.25 (2.93)		0.18 (3.08)
≥50	0.24 (3.57)		0.34 (3.35)
Sex^e
Female	0.33 (1.73)		0.19 (10.57)
Male	0.40 (3.63)		0.24 (3.42)
Education level		0.62		0.13
≤ 6th grade	0.36 (3.93)		0.29 (2.92)
7–11th grade	0.48 (2.91)		0.18 (4.51)
Country of birth		0.03		0.06
Costa Rica	0.31 (3.44)		0.21 (3.53)
Nicaragua	0.85 (2.87)		0.55 (2.78)
Poverty status		0.35		0.60
≤ Poverty line	0.25 (3.55)		0.35 (6.14)
> Poverty line	0.48 (3.43)		0.21 (2.87)
Handedness^e
Right	0.36 (3.41)		0.24 (3.61)
Left	2.20 (1.27)		0.24 (NA)
Years worked in agriculture^d		0.04		0.81
≤14	0.77 (3.17)		0.32 (4.40)
15–29	0.25 (3.30)		0.15 (2.38)
≥30	0.26 (3.17)		0.29 (3.72)
Type of farm		0.04		0.93
Conventional	0.24 (3.46)		0.25 (3.50)
Organic	0.56 (3.24)		0.24 (3.69)
Drinking water source^e
Aqueduct	0.40 (3.62)
Spring	0.26 (NA)		0.24 (3.61)
Other	0.70 (NA)		0.18 (NA)
Days between fNIRS and toenail/hair sample collection^d		0.12		0.71
< 30	0.61 (3.67)		0.32 (5.40)
≥30	0.26 (2.95)		0.20 (2.45)

Abbreviations: fNIRS, functional near-infrared spectroscopy; GM, geometric mean; GSD, geometric standard deviation; LOD, limit of detection; NA, not applicable.

37 farmworkers (92.5%) had toenail Mn concentrations above the LOD (0.05 μg/g).

30 farmworkers (90.1%) had hair Mn concentrations above the LOD (0.05 μg/g).

We estimated bivariate associations using Spearman correlation tests for continuous variables and Wilcoxon rank-sum tests for categorical variables.

Bivariate associations assessed using continuous variable.

Bivariate association not assessed due to small sample size.