1.06.B–T02 - Heavy Metal and Pesticide Exposure in African Elephants: A Study from Lower Zambezi, Zambia

Abstract

1. Introduction
Heavy metal and pesticide contamination present significant environmental challenges, particularly in regions experiencing increased anthropogenic activity [1]. Elephants are highly susceptible to the bioaccumulation of such toxicants due to their diverse plant-based diet and wide-ranging migratory behavior. Lower Zambezi National Park in Zambia, which is home to African savanna elephants and a variety of endemic wildlife species, has faced severe environmental threats from copper mining activities initiated in 2021. Although the government revoked the mining license in 2023 [2], significant ecological damage had already occurred [3], prompting concerns about potential contamination from heavy metals and pesticides. Hence the current study was designed to investigate the level of heavy metals and pesticides in elephants found in the lower Zambezi.
2. Materials and Methods
To assess heavy metal and pesticide exposure in elephants, we employed a non-invasive fecal sampling approach. Fecal samples were collected from two distinct zones of the park: 33 samples from the eastern zone in November 2022 and 74 samples from the western zone in September 2023, along with plant and soil samples for a different study were used for comparative analysis. The concentrations of essential and non-essential metals (Cr, Cd, Pb, As, Cu, Co, Ni, Zn) were quantified using inductively coupled plasma mass spectrometry (ICP-MS). Pesticide residues were analyzed via liquid chromatography–tandem mass spectrometry (LC-MS/MS) and gas chromatography–tandem mass spectrometry (GC-MS/MS).
3. Results and Discussion
3.1. Concentrations of essentials and non-essential metals
We observed notable spatial and temporal variation in heavy metal concentrations across fecal, soil, and plant samples. Concentrations of Pb, Co, Ni, and Cd showed statistically significant differences between 2022 and 2023, which 2022 sample showed the higher for Pb, Co and Cd. In 2023, fecal metal concentrations followed the descending order: Mn (122.8 mg/kg) > Zn (26.3) > Cu (9.1) > Ni (4.61) > Cr (3.77) > Co (0.82) > Pb (0.31) > As (0.30) > Cd (0.002). This order mirrored that found in plant samples but not soil, suggesting that plant ingestion (e.g., Acacia spp.) is the primary route of metal exposure. Fecal samples generally exhibited higher metal levels than plant samples, indicating bioaccumulation. In one 2023 fecal sample, exceptionally high levels of Cd, Pb, As, Cr, Co, and Cu were detected, implying possible localized exposure, possibly associated with tourism activity and seasonal differences. Hierarchical clustering analysis showed that ~70% of high-exposure individuals were female, suggesting sex-based differences in foraging or home-range behavior. However, these differences were not statistically significant.
3.2. Pesticide concentrations
Low levels of pesticide residues were detected. Organophosphates and carbamate insecticides commonly used in Indoor Residual Spraying (IRS)—such as Propoxur [4]—were identified in plant (Acacia bark) and low level in some elephant feces samples, confirming exposure. Although the sampling sites were located far from human settlements, the detection of malaria-control pesticides indicates extensive environmental contamination. This dispersion likely resulted from atmospheric deposition or hydrological transport through the Zambezi River.
4. Conclusion
Our findings highlight discrepancies in metal concentrations between feces, soil, and plant matrices. Elephant feces generally contained lower levels than soil but higher than plants. Most concentrations remained within permissible human exposure thresholds [5]. Considering that elephants consume 100–200 kg of vegetation daily, the absence of pesticide residues in most faecal samples likely reflects rapid metabolic elimination, primarily via urinary excretion, rather than a lack of exposure. Despite the discontinuation of mining operations, persistent detection of heavy metals and pesticide residues suggests continued environmental contamination. This study provides the first empirical evidence of xenobiotic metabolism capacity in large wild herbivores using fecal biomonitoring. Although fecal-based assessment offers a promising non-invasive approach, further research is required to establish its validity and sensitivity, particularly for pesticide exposure. Continued environmental monitoring in the Lower Zambezi National Park is essential for understanding long-term ecological risks and guiding effective wildlife conservation strategies.
 

Author(s)

Presenter: Kanami, Watanabe

Authors: 

Kanami Watanabe Hokkaido University Japan      Nelly Banda Hokkaido University Japan      Yared Beyene Hokkaido University Japan
Rio Doya Hokkaido University Japan      John Yabe Zambia University Zambia      Kaampwe MUZANDU University of Zambia Zambia      Andrew Kataba University of Zambia Zambia      Yoshinori IKENAKA Hokkaido University Japan      Shouta Nakayama Hokkaido University Japan      Mayumi Ishizuka Hokkaido University Japan