SEARCHCROSS-SECTIONALenvironmental health, public health

cross-sectional·environmental health, public health, agricultural science, toxicology·PMC10232542

Seasonal variation and risks of potentially toxic elements in agricultural lowlands of central Cameroon

Environmental Geochemistry and Health · 7 authors, 4 centres

AI SUMMARY

FIDELITY 88%

POPULATIONAgricultural lowland soils in four areas of Yaoundé, Cameroon (Mokolo, Nkolbisson, Ekounou, Ekoumdoum)

INTERVENTIONSeasonal comparison (dry season vs wet season) of soil sampling

COMPARISONConcentrations of Pb, Cd, Cu, Zn, Cr, Ni compared between dry and wet seasons and across four lowland areas

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TL;DR

This study assessed seasonal variation of potentially toxic elements (Pb, Cd, Cu, Zn, Cr, Ni) in agricultural lowland soils of Yaoundé, Cameroon. All metals showed significant spatial variation across areas, but only copper exhibited a significant seasonal effect. Although ecological risk was low overall, chromium contamination was widespread and one site (Ekoumdoum) showed strong pollution during the wet season, highlighting the need for farmer education and waste management interventions.

Full summary

3,846 CHARS

**Background:** Potentially toxic elements (PTEs) in agricultural soils pose environmental and health risks due to their persistence and bioaccumulation. In Yaoundé, Cameroon, lowland areas are major agricultural zones but also receive municipal waste and agrochemical runoff. Previous studies found moderate PTE contamination, but seasonal variation was poorly understood. This study assessed concentrations of Pb, Cd, Cu, Zn, Cr, and Ni in cultivated lowland soils during dry and wet seasons and evaluated pollution and ecological risk.

**Methods:** Soil samples (0–20 cm depth) were collected from four lowland areas (Mokolo, Nkolbisson, Ekounou, Ekoumdoum) in Yaoundé during July–August (short dry season) and September–October (short wet season) of 2019. Sixty composite samples were collected per season (10 in Mokolo, 12 in Nkolbisson, 16 in Ekounou, 22 in Ekoumdoum). Samples were air-dried, sieved (<0.25 mm), digested with aqua regia, and analyzed by ICP-OES. Quality control included reference materials (ISE 993 sandy soil) with ~75% recovery. Pollution was assessed using the single pollution index (SPI) and Nemerow composite pollution index (NCPI) against Finnish Ministry of Environment thresholds. Ecological risk was evaluated using Hakanson's potential ecological risk index (PERI). Statistical analysis used robust two-factor mixed-effects models with bootstrapping (Stata 15.1).

**Key Results:** Cd was below detection limits in all samples. Mean concentrations (mg/kg) varied by area and season. In Mokolo (dry season), Cu=122.2, Pb=65.1, Ni=31.4, Cr=133.5, Zn=276.6; in wet season, Cu=87.7, Pb=83.1, Ni=37.0, Cr=132.1, Zn=258.9. In Ekounou (dry), Cu=36.9, Pb=1.4, Ni=22.8, Cr=135.2, Zn=104.1; wet: Cu=41.2, Pb=3.6, Ni=21.9, Cr=147.1, Zn=89.6. In Ekoumdoum (dry), Cu=54.4, Pb=2.0, Ni=17.9, Cr=87.6, Zn=108.6; wet: Cu=44.8, Pb=4.0, Ni=15.2, Cr=103.6, Zn=92.4. In Nkolbisson (dry), Cu=59.7, Pb=8.8, Ni=16.9, Cr=106.1, Zn=114.4; wet: Cu=46.5, Pb=12.5, Ni=20.5, Cr=151.6, Zn=82.9. Cr exceeded the MEF threshold (100 mg/kg) in all areas during both seasons except Ekounou. Cu, Pb, and Zn exceeded thresholds only in Mokolo. Coefficient of variation was moderate for Zn (35%), Cr (42%), Cu (43%), Ni (46%) and high for Pb (85%). Mixed-effects models showed significant area effects for all elements (Cu: F=39.8, p<0.001; Cr: F=8.0, p=0.046; Ni: F=13.3, p=0.004; Pb: F=118.6, p<0.001; Zn: F=89.6, p<0.001), but seasonal effects were significant only for Cu (F=4.1, p=0.042). SPI values ranged from clean to slightly polluted (SPI 1–2) for most elements. NCPI indicated slight pollution (grade III) in most areas (range 1.0–1.7), except Ekoumdoum wet season which showed strong pollution (NCPI=5.0, grade V), driven by high Cr SPI. All Er values were <30 and PERI values were <100 across all areas and seasons, indicating low ecological risk. PERI was highest in Mokolo (dry: 18.7; wet: 18.9) and lowest in Ekounou (dry: 6.9; wet: 5.9).

**Clinical Implications:** While the ecological risk from PTEs in Yaoundé's lowland agricultural soils is currently low, the widespread chromium contamination and strong pollution at Ekoumdoum during the wet season warrant attention. The moderate-to-high variability of element concentrations points to anthropogenic sources (fertilizers, pesticides, waste, artisanal activities). The absence of Cd and the dominance of Cr as a contaminant differ from previous local studies, suggesting shifting contamination patterns. Farmer education on safe agrochemical use and improved urban waste management are needed. Regular monitoring and source-control measures (e.g., adjusting planting patterns, land-use types) could mitigate future health risks. The study serves as an early warning, and future research should track PTE transfer from soil to crops and assess human and livestock health risks.

PICO

PPOPULATION

Agricultural lowland soils in four areas of Yaoundé, Cameroon (Mokolo, Nkolbisson, Ekounou, Ekoumdoum)

IINTERVENTION

Seasonal comparison (dry season vs wet season) of soil sampling

OOUTCOME

Element concentrations (mg/kg), single pollution index (SPI), Nemerow composite pollution index (NCPI), single ecological risk (Er), and potential ecological risk index (PERI)

STUDY TYPE

cross-sectional

SPECIALTY

environmental health

SUMMARISED BY

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FIDELITY CHECK

88% · B

ORIGINAL PAPER

PMC10232542

Seasonal variation and risks of potentially toxic elements in agricultural lowlands of central Cameroon

Environmental Geochemistry and Health

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ABSTRACT

Abstract Intensive urban agriculture is expanding in Cameroon, which increases the risks of environmental pollution, particularly in the lowlands. This study assessed the seasonal characteristics of some potentially toxic elements and their ecological risks during the dry and wet seasons in urban agricultural soils in four lowlands in Yaoundé. The area and seasonal variation of some potentially toxic elements (Cu, Pb, Zn, Cd, Cr, and Ni) were evaluated using mixed-effects modeling. The pollution status of these elements in the soil was evaluated and interpreted using parameters such as the single pollution (SPI) and Nemerow composite pollution (NCPI) indices. In addition, the effect of these metals in the environment was assessed using the potential ecological risk index (PERI). The distribution of all the studied elements showed an area effect, while a seasonal effect was only noticeable for Cu. The concentration of Cu, Pb, and Zn was higher than the recommended threshold values in one of the areas sampled, while Cr exceeded these threshold values in all areas during both seasons. Cr exhibited the highest SPI among all studied elements during the dry and wet seasons in all areas. Except for the NCPI in one area, where grade V (strong) soil pollution was recorded during the wet season, the soil from all the study areas exhibited a slight pollution level (grade III) with a mean NCPI between 1 and 2. The PERI value of all areas was below the reference values during both seasons, suggesting an overall low potential contamination risk of the soil biota. The results indicate that preventive action to limit the heavy metal contamination in the lowlands of Yaoundé needs to be taken, for instance, through the promotion of more sustainable use of agrochemicals like pesticides and mineral fertilizers. Keywords: Agricultural soils, Potentially toxic elements, Pollution index, Ecological risk, Lowlands, Cameroon

CITATION EXPORT

Annie Stephanie Nana, Timo Falkenberg, Andrea Rechenburg et al.. Seasonal variation and risks of potentially toxic elements in agricultural lowlands of central Cameroon. Environmental Geochemistry and Health. (2023). https://doi.org/10.1007/s10653-022-01473-9

AUTHORS

7 · 4 CENTRES

Annie Stephanie Nana, Timo Falkenberg, Andrea Rechenburg, Joshua Ntajal, Juliet Wanjiku Kamau, Anne Ayo, Christian Borgemeister

1Center for Development Research (ZEF), University of Bonn, 53113 Bonn, Germany
2Laboratory of Biotechnology and Environment, Department of Plant Biology, Faculty of Science, University of Yaoundé I, 812 Yaoundé, Cameroon
3Institute of Hygiene and Public Health, Medical Faculty, University of Bonn, 53127 Bonn, Germany
4Department of Geography, University of Bonn, 53115 Bonn, Germany