Soil variability effect on the indices of potentially toxic elements pollution under the coffee (Coffea arabica)-enset (Ensete ventricosum) agroforestry systems of Southern Ethiopia

Overview

Ait Saghir and colleagues measured potentially toxic elements in surface soils under coffee-enset agroforestry systems in southern Ethiopia. This is in-scope supply-chain pathway and source-attribution evidence for agroforestry soil reservoirs and amendment-linked metal loading; it is not coffee-bean, enset, or finished-food occurrence evidence.

Key numbers

The abstract reports 46 surface soil samples analyzed by ICP-OES for total arsenic, lead, zinc, copper, manganese, barium, strontium, and titanium. Source-reported average concentrations across the study are:

Table 1 reports descriptive statistics by soil type, in mg/kg:

The source reports LOD and LOQ values in mg/kg: arsenic (As) LOD = 0.3 and LOQ = 1; Cu LOD = 0.3 and LOQ = 1; Ba LOD = 0.9 and LOQ = 3; lead (Pb) LOD = 0.3 and LOQ = 1; Zn LOD = 0.3 and LOQ = 1; Sr LOD = 0.3 and LOQ = 1; Mn LOD = 0.3 and LOQ = 1; Ti LOD = 0.3 and LOQ = 1.

Table 2 reports single pollution index values by soil type:

The abstract and conclusion highlight localized moderate contamination for Pb, with max SPI = 5.37 in Luvisols, Zn, with max SPI = 3.13 in Cambisols, and slight Cu contamination in Nitisols, with SPI = 2.66. Arsenic showed moderate contamination across soil types, including Luvisols where SPI = 1.53 and I-geo = 2.29 were reported.

Table 3 reports selected geoaccumulation-index values:

The enrichment-factor discussion reports Luvisols maximum EF values of 1.99 for Pb, 3.39 for Zn, 3.44 for Sr, and 1.97 for Mn. The authors attribute this localized enrichment to anthropogenic sources, especially intensive organic-matter amendments including manure and animal waste, with compost, poultry litter, sewage sludge, and household waste named as possible contributors.

Methods (brief)

The study sampled the Gedeo Zone of southern Ethiopia, a coffee-enset agroforestry region with Cambisols, Luvisols, and Nitisols. Forty-six surface composite soil samples were collected from 0-20 cm depth between 16 and 23 August 2023. Each composite consisted of 25 subsamples from approximately 250 m2, collected with a stainless-steel auger; about 1 kg fresh soil was collected per sampling point, GPS coordinates were recorded, and samples were air-dried, mixed, and sieved to 2 mm.

Soil pH, electrical conductivity, cation exchange capacity, total organic carbon, and particle-size distribution were measured using standard methods. Total potentially toxic elements were determined after 5 mL aqua-regia digestion and ICP-OES analysis following ISO 54320:2020. QA/QC included blanks, independent calibration standards, certified reference materials every ten samples, 5% duplicates, and 5% spikes at 1 mg/kg. Acceptance criteria included R2 >= 0.995, standard deviation ⇐ 5%, duplicate difference < 10%, and recoveries within +/- 10%; the authors state all results met these criteria.

Related evidence

• Soil-to-plant transfer of heavy metals
• Irrigation water and soil amendments as anthropogenic inputs to cropland
• Source attribution and environmental burden apportionment
• Arsenic
• Lead
• Copper
• Zinc
• Manganese
• Barium
• Titanium

Update history

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