INTERNATIONAL JOURNAL OF RESEARCH AND SCIENTIFIC INNOVATION (IJRSI)
ISSN No. 2321-2705 | DOI: 10.51244/IJRSI |Volume XII Issue X October 2025
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Evaluation of Human Health Risks Associated with Selected Heavy
Metal Exposure from Fumarolic Condensates in Mt. Suswa, Kenya
Gideon Yator*, Jackson John Kitetu, Caroline Chepkirui
Department of Physical and Biological Sciences, Kabarak University, P.O. Private Bag 20157, Nakuru -
Kenya.
* Corresponding author
DOI: https://dx.doi.org/10.51244/IJRSI.2025.1210000078
Received: 02 October 2025; Accepted: 08 October 2025; Published: 04 November 2025
ABSTRACT
Fumarolic condensates in volcanic terrains often serve as critical water sources for nearby communities but may
contain toxic heavy metals mobilized through magmatic degassing and hydrothermal leaching. This study
evaluated the potential human health risks associated with exposure to selected heavy metals (arsenic (As),
cadmium (Cd), lead (Pb), and mercury (Hg)) in fumarolic condensates from Mt. Suswa, Kenya. Condensate
samples were collected from ten modified fumarolic vents actively used by local residents and analyzed using
an Agilent 5110 ICP-OES for trace-metal quantification. The mean concentrations of As (3.86 ppb), Pb (1.43
ppb), and Cd (0.85 ppb) were all below World Health Organization (2022) and NEMA (2024) limits, while Hg
remained undetected in all samples. The Heavy Metal Pollution Index (HPI) and Heavy Metal Evaluation Index
(HEI) indicated moderate contamination (mean HPI = 20.46 ± 12.75; HEI = 0.70 ± 0.28), with higher enrichment
observed in inner-caldera fumaroles, reflecting stronger magmatic influence. Health-risk assessment following
USEPA (2011) methodology showed that non-carcinogenic hazard quotients (HQ) for As and Cd were below
unity for both adults and children, though relatively higher in children, indicating greater susceptibility to chronic
exposure. The carcinogenic risk (CR) for As ranged from 9.98 × 10⁻⁵ (F2) to 1.00 × 10⁻⁴ (F4) for adults and 9.78
× 10⁻⁵ (F10) to 1.92 × 10⁻⁵ (F6) for children, with the former slightly exceeding the upper USEPA threshold
(10⁻⁶–10⁻⁴), suggesting a low but notable lifetime cancer probability from prolonged exposure. Although overall
contamination levels were low, localized enrichment and cumulative exposure may pose health risks to
vulnerable populations. These findings underscore the importance of continuous monitoring, community
education, and sustainable mitigation strategies such as alternative safe-water supplies and affordable point-of-
use treatment technologies in geothermal-affected regions.
Keywords: Mt. Suswa, fumarolic condensates, heavy metals, human health risk
INTRODUCTION
Geothermal and volcanic regions are characterized by extensive hydrothermal activity that releases gases and
condensates enriched with various trace elements and heavy metals. These condensates often provide vital
freshwater sources for surrounding communities, especially in arid or semi-arid volcanic terrains where
alternative supplies are limited. However, geothermal fluids commonly carry toxic metals such as arsenic (As),
cadmium (Cd), lead (Pb), and mercury (Hg), which originate from magmatic degassing, mineral dissolution, and
rock–water interactions (Ayari et al., 2023; Yao et al., 2024). When these metals enter fumarolic waters, they can
accumulate in biota or drinking-water systems, posing long-term health threats even at trace concentrations
(Durowoju et al., 2020; Sunguti et al., 2024)
Globally, geothermal fields such as Rotorua (New Zealand), Aluto–Langano (Ethiopia), and Larderello (Italy)
have been shown to contain elevated levels of As, Cd, and Pb in geothermal discharges that exceed international
drinking-water limits(Morales-deAvila et al., 2023; Sanjuan, 2024). Chronic ingestion or inhalation of these
metals has been linked to systemic and carcinogenic health effects, including skin lesions and keratosis, renal
tubular dysfunction, neurological impairment, and various cancers (Charkiewicz et al., 2023; kaur et al., 2024).
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The World Health Organization (WHO, 2022) and USEPA, (2011) have established permissible guideline values
and risk-assessment frameworks to quantify both non-carcinogenic (hazard quotient, HQ) and carcinogenic
(cancer risk, CR) indices for metals of public-health concern.
Within Africa, the East African Rift System (EARS) holds vast geothermal potential, with Kenya, Ethiopia, and
Tanzania at the forefront of its development (Elbarbary et al., 2022). However, comprehensive research on heavy
metal contamination and its health risks from these geothermal sources are limited, leaving a significant
knowledge gap in understanding the environmental impacts of geothermal activities in the region. In Kenya,
fumarolic and hydrothermal features occur widely along the Central Kenya Rift, including Olkaria, Eburru,
Longonot, Menengai, and Mt. Suswa (Mangi, 2016).
Mt. Suswa, located in the southern segment of the Kenya Rift Valley approximately 120 km northwest of Nairobi,
is characterized by a unique double-caldera structure with active fumaroles and extensive geothermal
manifestations. Communities residing around Mt. Suswa depend heavily on condensed geothermal steam from
fumarolic vents for domestic water needs (Mohamud, 2013). Beyond its geothermal potential, the study area
supports Maasai pastoralist livelihoods and possesses high ecological and cultural significance, making the
balance between geothermal development, environmental protection, and community health critically important.
Local residents use fumarolic condensates for drinking, bathing, cooking, and watering livestock, thereby
increasing potential exposure to heavy-metal contaminants (Masikonte, 2020). Yet, systematic evaluations of
heavy-metal contamination and associated health impacts in the Mt. Suswa area remain limited or nonexistent.
Consequently, baseline data to support environmental monitoring, community health protection, and sustainable
geothermal resource management are lacking.
This study therefore aimed to evaluate the potential human health risks associated with exposure to selected
heavy metals (As, Cd, Pb, and Hg) in fumarolic condensates from Mt. Suswa, Kenya. By linking geochemical
data with quantitative health-risk metrics, the study provides essential baseline information for the Mt. Suswa
geothermal prospect and enhances understanding of heavy-metal exposure pathways within the broader East
African Rift System.
METHODOLOGY
Study Area and Geology
Mt. Suswa, the southernmost Quaternary volcano along the axis of the Central Kenya Rift, is bounded by
latitudes 1.00°S–1.18°S and longitudes 36.13°E–36.33°E. It lies approximately 120 km northwest of Nairobi
and represents one of Kenya’s most distinctive volcanic structures (Fig. 1). The mountain is a Quaternary
trachytic shield volcano characterized by a unique double-caldera system consisting of an inner caldera, about 4
km in diameter, enclosed within an outer caldera measuring roughly 12 × 8 km, with the rim reaching an
elevation of 1,890 m above sea level. The volcano rises nearly 800 m above the Rift Valley floor, attaining a
maximum elevation of 2,356 m, and covers an estimated area of over 700 km² (Nyairo et al., 2014).
Geologically, Mt. Suswa is composed predominantly of trachytic, and basaltic lavas, interbedded with tuffs,
pyroclastic deposits, and volcanic breccias. These lithologies form the structural and hydrological framework
that hosts a vapor-dominated geothermal system. Fumarolic activity is concentrated along ring faults and fracture
zones associated with caldera collapse and resurgence (Mohamud, 2013).
The broader Mt. Suswa prospect exhibits active fumarolic emissions and the surrounding terrain is semi-arid and
inhabited primarily by Maasai pastoralist communities, who rely heavily on condensed fumarolic steam for
domestic water use due to limited access to conventional freshwater sources.
INTERNATIONAL JOURNAL OF RESEARCH AND SCIENTIFIC INNOVATION (IJRSI)
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Fig 1: Location and sampling sites of fumarolic vents in the Mt. Suswa area
Sample Collection and Preparation
Condensate samples were obtained from ten (10) modified fumarolic vents actively used by the local community
within the Mt. Suswa geothermal area. Sampling was conducted during the early morning hours to minimize
evaporation losses and airborne contamination. At each site, condensates were collected directly from
condensation pipes into pre-acid-washed 500 mL high-density polyethylene (HDPE) bottles.
To ensure analytical reliability, duplicate samples were collected from each fumarole during every sampling
event. One bottle was immediately acidified in the field with 1 mL of concentrated nitric acid (HNO₃) to lower
the pH to < 2, preventing metal adsorption onto container walls and preserving dissolved elements for trace-
metal analysis. The second bottle was used for in situ measurement of physico-chemical parameters, including
temperature (°C), pH, electrical conductivity (EC, µS/cm), and total dissolved solids (TDS, mg/L).
Temperature measurements were performed using a Hanna HI-935002 thermocouple thermometer (Woonsocket,
USA), while pH and EC were determined using a Jenway 430 pH/Conductivity meter (London, UK). All samples
were carefully sealed, labeled, and stored at 4°C in insulated coolers to preserve their integrity prior to laboratory
analysis.
Sample Analysis
Water Quality Assessment
Basic physico-chemical parameters (pH, EC, TDS) were analyzed following the American Public Health
Association (APHA, 2022) standard methods. Results were compared against World Health Organization
(WHO, 2022) and Kenya’s National Environment Management Authority (NEMA, 2024) drinking-water
guideline values to assess compliance and suitability for domestic use.
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Heavy-Metal Analysis and Quality Control
Concentrations of arsenic (As), lead (Pb), cadmium (Cd), and mercury (Hg) were quantified using an Agilent
5110 Inductively Coupled Plasma–Optical Emission Spectrometer (ICP-OES) at the Kenya Bureau of Standards
(KEBS) Laboratory. Calibration standards (0, 5, 10, 25, 50 ppb) were prepared from certified 1000 mg/L stock
solutions. Instrument calibration curves exhibited correlation coefficients (R²) ≥ 0.999. Analytical precision and
accuracy were verified through reagent blanks, matrix spikes, and triplicate determinations. Method detection
limits (MDLs) were 0.01 µg/L for As, 0.02 µg/L for Pb, 0.01 µg/L for Cd, and 0.05 µg/L for Hg. Recovery rates
ranged from 98% to 103%, ensuring analytical reliability.
Compositional Indices
Heavy Metal Pollution Index (HPI)
The Heavy Metal Pollution Index (HPI) was used to assess the overall quality of the fumarolic condensates based
on the combined effect of multiple heavy metals. The HPI provides a composite measure that indicates the degree
of heavy-metal contamination relative to standard permissible limits. The HPI was computed using the weighted
arithmetic mean model as described by Eldaw et al., (2020) ;
������ =
∑(W��Q��)
∑W��
………............................ (1)
where:
���� =
(����−����)
(����−����)
X 100 ………........................(2)
and
Mi = Measured concentration of the ith metal (µg/L),
Ii = Ideal value (zero for all metals),
Si = Standard permissible value (WHO, 2022),
Wi = Unit weight assigned to each metal, inversely proportional to Si.
Wi =
��
����
………………………… (3)
where K is a constant of proportionality ensuring normalization of the weighting factors.
Interpretation of the computed HPI values was based on established threshold ranges, where:
HPI < 50: low heavy-metal pollution (acceptable quality)
HPI = 50–100: moderate contamination
HPI > 100: high contamination or potential health concern
(Ahmed et al., 2023; Kumar & Maurya, 2025)
Heavy Metal Evaluation Index (HEI)
The Heavy Metal Evaluation Index (HEI) was also applied to assess the cumulative contamination level of the
fumarolic condensates by integrating the concentrations of all analyzed metals relative to their respective
permissible limits. This index provides a straightforward measure of overall heavy-metal load within a sample,
reflecting both the magnitude and collective contribution of multiple contaminants. The HEI was computed
following the approach of Brraich & Jassal, (2021), as expressed by:
INTERNATIONAL JOURNAL OF RESEARCH AND SCIENTIFIC INNOVATION (IJRSI)
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HEI = ∑
����
����
………………….…. (4)
where
Ci = Measured concentration of the ith metal (µg/L),
Si = Corresponding standard permissible concentration(WHO, 2022).
Interpretation of HEI values was based on the following classification criteria:
HEI < 1: low contamination (negligible impact)
HEI = 1–10: moderate contamination
HEI > 10: high contamination (significant pollution potential)
These indices were applied to determine the overall extent of metal enrichment and to identify spatial variations
in contamination intensity, aligning with recent studies that have employed HPI and HEI to evaluate multi-metal
pollution patterns and cumulative water quality degradation in aquatic environments (Tokatli, 2024; Wu et al.,
2024)
Human Health Risk Assessment
The health risk assessment was conducted using the United States Environmental Protection Agency (USEPA,
2011) risk assessment framework. Non-carcinogenic risks were evaluated using the Hazard Quotient (HQ) for
individual metals and the Hazard Index (HI) for cumulative effects, while carcinogenic risks were quantified
using the Lifetime Cancer Risk (LCR) model. The exposure pathways considered in this analysis included both
ingestion and dermal absorption, as these represent the primary routes of human exposure to fumarolic
condensates in the Suswa community. All the parameters for calculations are summarized in Table 1 below;
(i) Ingestion Pathway
The Lifetime Cancer Risk via ingestion was estimated using Equation 8:
LCRingestion = EDIingestion + SF……………………………………… (5)
Where:
LCRingestion = Lifetime Cancer Risk from ingestion exposure.
EDIingestion = Estimated Daily Intake via ingestion (mg/kg/day), calculated using Equation 6
������������������������ =
���� �� ���� �� ���� �� ����
���� �� ����
………………………………………… (6)
(ii) Dermal Pathway
The Lifetime Cancer Risk via dermal absorption was calculated using Equation 7 and 8:
LCRdermal = EDIdermal + SF…………………………………………… (7)
LCRdermal = Lifetime Cancer Risk from dermal exposure.
EDIdermal = Estimated Daily Intake via dermal absorption (mg/kg/day), calculated using:
������������������ =
���� �� ���� �� ���� �� ���� �� ���� �� ���� �� ����
���� �� ����
………………………………. (8)
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Table 1: Parameters and Their Sources for HPI, HEI, HQ, HI, and CR Calculations
Parameter Symbol Unit Description Source
Metal
concentration
(Ci) or (Mi) µg/L (ppb) Measured concentration of
metal (As, Cd, Pb, Hg) in
fumarolic condensates
This study (Agilent 5110
ICP-OES results)
Standard
permissible limit
(Si) µg/L WHO and NEMA guideline
values for safe drinking water
WHO (2022); NEMA
(2019)
Ideal value (Ii ) µg/L Ideal (zero) concentration for
metals in pure water
(Kowalska et al., 2018);
USEPA (2011)
Unit weight (Wi) — Weight assigned inversely
proportional to permissible limit
((Wi = 1/ Si))
(Kowalska et al., 2018)
Sub-index for HPI (Qi) — Metal quality rating; (Qi = ((Mi
- Ii)/( Si - Ii)) \times 100 )
Kowalska et al., 2018)
Heavy Metal
Pollution Index
HPI — Overall degree of heavy metal
contamination
(Anitha et al., 2021)
Heavy Metal
Evaluation Index
HEI — Summation of ratios of
concentration to standard limits;
( HEI = \sum (C_i/S_i) )
(Prasad & Bose, 2001)
Estimated Daily
Intake
EDI mg/kg/day Intake of metal through
ingestion pathway; (EDI = (Cw
× IR × EF × ED)/(BW × AT) )
USEPA (2011)
Ingestion rate IR L/day Volume of condensate
consumed per day (2 for adults;
1 for children)
USEPA (2011)
Exposure
frequency
EF days/year Days per year of exposure (365) USEPA (2011)
Exposure duration ED years Period of exposure (30 for
adults; 6 for children)
USEPA (2011)
Body weight BW kg Average human body mass (70
for adults; 15 for children)
USEPA (2011)
Averaging time
(non-carcinogenic)
ATₙ days ED × 365 USEPA (2011)
Averaging time
(carcinogenic)
ATc days 70 × 365 (lifetime exposure) USEPA (2011)
Oral reference
dose
RfD mg/kg/day Acceptable daily intake for As =
3×10⁻⁴, Cd = 1×10⁻³
USEPA (2011)
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Cancer slope factor CSF (mg/kg/day)
⁻¹
Factor for carcinogenic
potential; As = 1.5; Cd = 6.3
USEPA (2011)
Hazard Quotient HQ — Ratio of EDI to RfD; (HQ = EDI
/ RfD)
USEPA (2011)
Hazard Index HI — Sum of HQs for multiple metals;
(HI = \sum HQi)
USEPA (2011)
Carcinogenic Risk CR — Lifetime probability of cancer;
(CR = EDI × CSF)
USEPA (2011); Rahman et
al. (2019)
Total Cancer Risk and Interpretation
The overall cumulative cancer risk from exposure to carcinogenic heavy metals in fumarolic condensates was
estimated by summing the Lifetime Cancer Risks (LCR) from all relevant pathways, namely ingestion and
dermal absorption. This total risk provided a comprehensive estimate of the lifetime probability of developing
cancer as a result of chronic exposure to contaminants in the fumarolic condensates. The calculation was
performed using Equation 9:
LCRTotal = LCRingestion + LCRdermal………………………………….………. (9)
Where:
LCRTotal : Total Lifetime Cancer Risk (unitless probability).
LCRingestion : Lifetime Cancer Risk from ingestion exposure.
LCRdermal : Lifetime Cancer Risk from dermal exposure.
The total cancer risk therefore represented the cumulative probability of an individual developing cancer over a
lifetime due to simultaneous exposure to heavy metals through both ingestion and dermal pathways (Raad et al.,
2021;USEPA, 2011)
Non-carcinogenic risks were assessed using the Hazard Quotient (HQ) and Hazard Index (HI). An HQ or HI
value greater than one (>1) indicated potential health concerns associated with exposure to a given contaminant
or combined contaminants. Carcinogenic risks, expressed as LCR values, were interpreted against the thresholds
recommended by USEPA, (2011). Risks below LCR < 1 × 10⁻⁶ were considered negligible, while risks LCR ≥
1 × 10⁻⁴ were considered unacceptable. Risks falling within the range of 10⁻⁶ ≤LCR < 10⁻⁴ were regarded as
tolerable but requiring careful monitoring and, where possible, mitigation measures (Demissie et al., 2024;
USEPA, 2011).
Non-carcinogenic risk
HQi =
EDI��
RfD��
………………........................(10)
LCRTotal = ∑������…………………………. (11)
Where RfDi is the reference dose for metal i. HQ or HI > 1 indicates potential concern.
Statistical Analysis
All analyses were conducted in triplicate, and results were expressed as mean ± standard deviation (SD).
Quantitative data obtained from laboratory and field analyses were subjected to descriptive statistics (mean,
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range, and standard deviation) to summarize the contamination levels and physico-chemical characteristics of
fumarolic condensates across different vents within the study area.
To evaluate variations in contaminant concentrations among fumarolic vents, inferential statistical tests,
including a one-way analysis of variance (ANOVA), were applied where assumptions of normality and
homogeneity of variance were satisfied (Mukwevho et al., 2025). Statistical analyses were performed using
SPSS version 26.0 and significance was determined at p < 0.05.
RESULTS AND INTERPRETATION
Heavy Metal Concentration in Fumarolic Condensates
The physico-chemical parameters and heavy-metal concentrations of fumarolic condensates from the Mt. Suswa
geothermal area are summarized in Table 2 below. The condensates exhibited near-neutral to slightly acidic pH
values (5.52–7.26; mean = 6.50 ± 0.42), consistent with weakly acidic conditions resulting from the dissolution
of magmatic gases such as CO₂ and SO₂ in condensate water. Temperatures ranged from 51.4 °C to 74.3 °C
(mean = 63.2 ± 7.2 °C), with higher temperatures observed in vents located within the inner caldera. Electrical
conductivity (EC) and total dissolved solids (TDS) varied between 5.16–51.22 µS/cm and 2.58–25.6 ppm,
respectively, indicating low mineralization typical of dilute hydrothermal condensates formed by steam
condensation of meteoric water.
The selected heavy-metal concentrations showed noticeable spatial variability (Table 2). Arsenic (As) ranged
from 2.24 to 5.49 ppb (mean = 3.86 ± 1.05 ppb), while lead (Pb) ranged between 0.95 and 1.98 ppb (mean =
1.43 ± 0.31 ppb). Cadmium (Cd) concentrations were generally low, detected only in six fumaroles (0.39–1.41
ppb; mean = 0.84 ± 0.34 ppb), whereas mercury (Hg) was below detection limits in all samples. All mean
concentrations were below the WHO (2022) and NEMA (2024) permissible limits for drinking water, implying
that fumarolic condensates were of acceptable chemical quality despite minor geogenic enrichment.
Spatially, fumaroles F9 and F10 exhibited the highest concentrations of As and Cd, corresponding to sites of
elevated temperature and vapor discharge near the inner-caldera vent system. This spatial pattern suggests that
elevated temperature enhances rock-steam interaction and leaching of volatile trace elements from
hydrothermally altered minerals.
Table 2: Physico-chemical parameters and heavy-metal concentrations (mean ± RSD %) in fumarolic
condensates from the Mt. Suswa geothermal area.
S. No
Sample
Map
Latitude Longitude pH/T°C
EC TDS As Pb Cd Hg
µS (ppm±%) Mean ±SD (ppb±%)
F1 F1 -1.227821 36.388119 7.19/51.4 14.72 7.36 4.86 ± 0.20 1.42 ± 0.09 ND ND
F2 F2 -1.211764 36.382253 7.26/58.2 5.16 2.58 3.21 ± 0.23 1.30 ± 0.07 0.53 ± 0.06 ND
F3 F3 -1.237729 36.354751 6.68/53.1 13.07 6.58 4.94 ± 0.10 1.53 ± 0.17 0.82 ± 0.09 ND
F4 F4 -1.238985 36.354498 6.94/64.6 17.01 8.52 3.82 ± 0.34 1.38 ± 0.11 0.39 ± 0.02 ND
F5 F6 -1.185491 36.32553 6.36/64.1 18.73 9.37 2.55 ± 0.28 1.35 ± 0.05 ND ND
F6 F7 -1.138952 36.329659 7.12/63.2 17.33 8.67 2.24 ± 0.16 0.95 ± 0.13 ND ND
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F7 F10 -1.118744 36.328995 6.44/54.4 11.92 5.96 3.13 ± 0.06 1.62 ± 0.05 ND ND
F8 F14 -1.12676 36.338155 6.19/71.2 22.41 11.2 3.32 ± 0.10 1.98 ± 0.08 0.68 ± 0.02 ND
F9 F18 -1.124473 36.338121 6.43/73.5 51.22 25.6 5.07 ± 0.46 1.27 ± 0.08 1.22 ± 0.05 ND
F10 F20 -1.12238 36.34202 5.52/74.3 21.15 10.54 5.49 ± 0.22 1.52 ± 0.05 1.41 ± 0.11 ND
NEMA Limit 6.5–8.5 NS 1200 10 50 10 1
WHO Limit 6.5–8.0 NS 1000 10 10 3 5
Note: Values are represented as Mean ±SD from triplicate analyses; ND = Not Detected; NS = Not Specified.
Hg was below the detection limit of 0.01 ppb in all samples.
The variability in trace-metal concentrations across fumaroles indicates the influence of localized geothermal
intensity and fluid-rock interactions, warranting evaluation of potential health implications through exposure
and risk indices.
Estimated Daily Intake (EDI)
The estimated daily intake (EDI) quantifies the potential exposure of individuals consuming fumarolic
condensates. Using USEPA (2011) exposure parameters, the EDI for adults ranged from 1.0 × 10⁻⁵ to 1.2 × 10⁻⁴
mg/kg/day for As and 0.5 × 10⁻⁵ to 4.3 × 10⁻⁵ mg/kg/day for Pb as shown in Table 3 below. Children had
proportionally higher EDI values, approximately 2.5–3 times those of adults due to lower body mass and higher
intake rates per kilogram body weight.
All EDI values were below their corresponding reference doses (RfD), implying minimal immediate
toxicological risk, although As exposure in children approached the RfD threshold.
Table 3: Estimated Daily Intake (EDI; mg/kg/day) of heavy metals in fumarolic condensates.
Metal Adults Children RfD (mg/kg/day) Interpretation
As 1.2 × 10⁻⁴ 3.0 × 10⁻⁴ 3.0 × 10⁻⁴ Marginal for children
Pb 4.3 × 10⁻⁵ 1.1 × 10⁻⁴ 3.5 × 10⁻³ Safe
Cd 1.6 × 10⁻⁵ 4.0 × 10⁻⁵ 1.0 × 10⁻³ Safe
Hg ND ND 3.0 × 10⁻⁴ Not detected
Human Health Risk Assessment
Non-Carcinogenic Risk (HQ and HI)
The Hazard Quotient (HQ) and cumulative Hazard Index (HI) were computed to assess non-carcinogenic risks
associated with ingestion of fumarolic condensates. All HQ values for adults were below unity, indicating no
significant health effects from individual metals. In children, HQ values for arsenic ranged from 0.45 to 0.98 in
high-temperature fumaroles (F9 and F10), suggesting marginal concern. The mean HI values of 0.36 for adults
and 0.80 for children were both below the critical threshold of 1, denoting negligible to low health risk. However,
the higher HQ values in children reflect their greater vulnerability due to lower body mass and higher water
intake per kilogram of body weight.
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These findings are summarized in Table 4, which presents the range and mean HQ values for each metal and the
cumulative HI for both adults and children. The results confirm that exposure to arsenic poses the greatest
relative contribution to non-carcinogenic risk, particularly among children living near high-temperature
fumaroles.
Table 4: Hazard Quotient (HQ) and Cumulative Hazard Quotient (CHQ) for adults and children in fumarolic
condensates from Mt. Suswa.
Metal Min HQ
(Adults)
Max HQ
(Adults)
Mean HQ
(Adults)
Min HQ
(Child)
Max HQ
(Child)
Mean HQ
(Child)
Interpretation
As 0.21 0.45 0.32 0.45 0.98 0.68 Marginal risk in
hot vents for
children; safe for
adults
Pb 0.01 0.02 0.02 0.05 0.12 0.08 Safe for both
groups
Cd 0.01 0.03 0.02 0.02 0.05 0.04 Safe for both
groups
HI
(∑HQ)
— — 0.36 — — 0.8 Within acceptable
limit for adults;
near threshold for
children
Carcinogenic Risk (CR)
Carcinogenic risk, expressed as the Lifetime Cancer Risk (LCR), was assessed for arsenic (As) and cadmium
(Cd) using their respective cancer slope factors of 1.5 and 6.3 (mg kg⁻¹ day⁻¹)⁻¹ as prescribed by the United
States Environmental Protection Agency (USEPA, 2011). The computed LCR values for adults ranged from 4.1
× 10⁻⁵ to 2.1 × 10⁻⁴, whereas those for children varied between 1.9 × 10⁻⁵ and 9.8 × 10⁻⁵. Most of these values
fall within the USEPA’s acceptable carcinogenic risk range (10⁻⁶–10⁻⁴), indicating generally low health risks
associated with long-term exposure to the fumarolic condensates.
As summarized in Table 5, arsenic contributed the highest proportion of the total cancer risk across all fumaroles,
reflecting its elevated geochemical mobility and strong affinity for geothermal vapor transport. Cadmium played
a lesser but noticeable role in enhancing total risk where it was detectable (notably at F3, F8–F10). The mean
total LCR for adults (7.6 × 10⁻⁵) and for children (1.8 × 10⁻⁴) remained within or marginally above the acceptable
threshold, with the highest values recorded at fumaroles F9 and F10, both located in the inner caldera where
elevated temperature and gas flux intensify trace-metal mobilization.
The findings suggest that the carcinogenic risk from fumarolic condensates in Mt. Suswa is generally acceptable,
though localized elevated LCRs at hot vents highlight the need for continued monitoring and community-level
mitigation such as point-of-use treatment, controlled exposure, and public awareness programs.
Table 5: Lifetime Cancer Risk (LCR) of heavy metals in fumarolic condensates for adults and children by
sampling site.
Fumarole As (Adults) Cd (Adults) LCRTotal (Adults) As (Child) Cd (Child) LCRTotal (Child) Interpretation
F1 8.93 × 10⁻⁵ 0 8.93 × 10⁻⁵ 4.17 × 10⁻⁵ 0 4.17 × 10⁻⁵ Acceptable
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F2 5.90 × 10⁻⁵ 4.09 × 10⁻⁵ 9.98 × 10⁻⁵ 2.75 × 10⁻⁵ 1.91 × 10⁻⁵ 4.66 × 10⁻⁵ Acceptable
F3 9.07 × 10⁻⁵ 6.33 × 10⁻⁵ 1.54 × 10⁻⁴ 4.23 × 10⁻⁵ 2.95 × 10⁻⁵ 7.19 × 10⁻⁵ Elevated concern
F4 7.02 × 10⁻⁵ 3.01 × 10⁻⁵ 1.00 × 10⁻⁴ 3.27 × 10⁻⁵ 1.40 × 10⁻⁵ 4.68 × 10⁻⁵ Marginal concern
F5 4.68 × 10⁻⁵ 0 4.68 × 10⁻⁵ 2.19 × 10⁻⁵ 0 2.19 × 10⁻⁵ Acceptable
F6 4.11 × 10⁻⁵ 0 4.11 × 10⁻⁵ 1.92 × 10⁻⁵ 0 1.92 × 10⁻⁵ Acceptable
F7 5.75 × 10⁻⁵ 0 5.75 × 10⁻⁵ 2.68 × 10⁻⁵ 0 2.68 × 10⁻⁵ Acceptable
F8 6.10 × 10⁻⁵ 5.25 × 10⁻⁵ 1.13 × 10⁻⁴ 2.85 × 10⁻⁵ 2.45 × 10⁻⁵ 5.29 × 10⁻⁵ Elevated concern
F9 9.31 × 10⁻⁵ 9.41 × 10⁻⁵ 1.87 × 10⁻⁴ 4.35 × 10⁻⁵ 4.39 × 10⁻⁵ 8.74 × 10⁻⁵ Elevated concern
F10 1.01 × 10⁻⁴ 1.09 × 10⁻⁴ 2.10 × 10⁻⁴ 4.71 × 10⁻⁵ 5.08 × 10⁻⁵ 9.78 × 10⁻⁵ Elevated concern
Mean 6.90 × 10⁻⁵ 7.70 × 10⁻⁶ 7.60 × 10⁻⁵ 1.60 × 10⁻⁴ 2.10 × 10⁻⁵ 1.80 × 10⁻⁴
Generally
acceptable;
marginal at hot
vents
Compositional Indices (HPI and HEI)
The Heavy-Metal Pollution Index (HPI) and Heavy-Metal Evaluation Index (HEI) were computed using the
WHO (2022) permissible limits for arsenic (10 µg/L), lead (10 µg/L), and cadmium (3 µg/L) to evaluate the
cumulative metal burden in fumarolic condensates. The HPI values ranged from 5.98 to 42.57, all below the
critical threshold of 50, indicating low overall contamination. Correspondingly, HEI values varied between 0.32
and 1.17, suggesting low to moderate heavy-metal load across the fumarolic field.
As summarized in Table 6, fumaroles F9 and F10 exhibited the highest HPI and HEI values, corresponding to
localized enrichment of arsenic and cadmium in high-temperature vents. These sites are situated near the inner
caldera, where intense geothermal activity enhances rock–steam interactions and metal volatilization. The mean
HPI (20.76) and mean HEI (0.74) classify the fumarolic condensates as acceptable in quality, though with minor
geogenic enrichment indicative of hydrothermal contribution. The overall results demonstrate spatial variability
consistent with temperature gradients and vapor flux intensity within the Suswa geothermal system.
Table 6: Heavy-Metal Pollution Index (HPI) and Heavy-Metal Evaluation Index (HEI) for fumarolic condensates
(Mt. Suswa).
Fumarole HPI HEI Interpretation
F1 11.78 0.63 Low pollution
F2 19.53 0.63 Low pollution
F3 29.20 0.92 Low–moderate
F4 17.88 0.65 Low pollution
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F5 7.31 0.39 Very low
F6 5.98 0.32 Very low
F7 8.91 0.48 Low
F8 24.12 0.76 Low–moderate
F9 37.33 1.04 Moderate
F10 42.57 1.17 Moderate
Mean 20.46± 12.75 0.70± 0.28 Low–moderate overall
The fumarolic condensates from Mt. Suswa exhibit low to moderate heavy-metal contamination, with As and Pb
being the dominant elements of concern. The observed metal levels are below WHO and NEMA thresholds,
confirming that the condensates are chemically suitable for domestic use after minor treatment.
However, spatially elevated HPI and HEI values in the inner-caldera fumaroles (F9 and F10) indicate localized
enrichment influenced by higher temperature and prolonged water-rock interaction. Health-risk assessment
revealed that non-carcinogenic risks are minimal (HQ < 1) but potential carcinogenic risks from As in children
(LCR ≈ 1 × 10⁻⁴) merit attention.
Overall, the integrated indices (EDI, HQ, HI, LCR, HPI, HEI) reveal that Mt. Suswa fumarolic condensates are
generally of acceptable chemical quality. However, localized enrichment in As and Cd at inner-caldera vents
(F9, F10) suggests elevated geothermal input, emphasizing the need for targeted monitoring and preventive
exposure control.
DISCUSSION AND FINDINGS
Heavy Metal Levels in Fumaroles
The fumarolic condensates from Mt. Suswa exhibited near-neutral to slightly acidic pH values (5.52–7.26; mean
= 6.50 ± 0.42), consistent with mild acidification caused by the dissolution of magmatic gases such as CO₂ and
SO₂ in meteoric water. Similar processes have been documented in recent studies where fumarolic gas–water
interactions generate weakly acidic condensates through magmatic gas dissolution (Obase et al., 2022; Yaguchi
et al., 2025). The condensate temperatures, ranging between 51.4 °C and 74.3 °C, align with shallow steam
discharge in active geothermal systems, and the particularly high temperatures in inner-caldera vents reflect
intensified magmatic–hydrothermal activity (Agusto et al., 2023; Campeny et al., 2023). Electrical conductivity
(EC) and total dissolved solids (TDS) varied from 5.16–51.22 µS/cm and 2.58–25.6 ppm, respectively, denoting
low mineralization typical of dilute hydrothermal condensates derived from condensed steam rather than deep
geothermal brines.
Concentrations of heavy metals exhibited distinct spatial variability across fumarolic vents in Mt. Suswa (Table
2). Arsenic (As) ranged between 2.24–5.49 ppb (mean = 3.86 ± 1.05 ppb), lead (Pb) varied from 0.95–1.98 ppb
(mean = 1.43 ± 0.31 ppb), and cadmium (Cd) from 0.39–1.41 ppb (mean = 0.84 ± 0.34 ppb), while mercury (Hg)
remained below detection limits in all samples. These trace-element concentrations are considerably lower than
the WHO (2022) and NEMA (2024) permissible limits for drinking water (As = 10 µg/L, Pb = 10 µg/L, Cd = 3
µg/L), suggesting that the condensates are chemically safe despite localized enrichment within inner-caldera
vents. Comparable patterns of spatial heterogeneity in fumarolic trace-metal composition have been documented
in other active volcanic systems, where elevated As, Pb, and Cd near high-temperature vents are linked to vapor-
phase transport and rock-steam interaction (Campeny et al., 2023; Inostroza et al., 2022; Werner et al., 2020).
Such variations reflect geothermal intensity and proximity to magmatic conduits, which control the geochemical
partitioning of metals within condensate fluids (Inostroza et al., 2022)
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Spatially, vents F9 and F10 exhibited the highest As and Cd concentrations, co-occurring with hotter discharge
zones—an association consistent with intensified rock–steam exchange and leaching of volatile trace metals
from hydrothermally altered minerals under elevated thermal and vapor flux conditions (Sunguti et al., 2024).
The site-specific index values at these vents (HPI = 37.33–42.57; HEI = 1.04–1.17) corroborate localized heavy-
metal enrichment, whereas the overall means (HPI = 20.76; HEI = 0.74) indicate low-to-moderate pollution in
line with recent applications of HPI/HEI for water-quality evaluation (Badeenezhad et al., 2023; Biedunkova &
Kuznietsov, 2024). As summarized in Table 6, the fumarolic condensates at Mt. Suswa are therefore of
acceptable chemical quality for potential domestic use when judged against contemporary guideline values, with
only minor geogenic enrichment in inner-caldera vents; the slight acidity observed is typical of vapor-heated
systems and can be mitigated by simple neutralization or blending before use (Sunguti et al., 2024; WHO, 2022).
Table 6. Comparison of Physico-Chemical Parameters with WHO and NEMA Standards
Parameter Mean (This Study) WHO (2022)
Limit
NEMA (2024)
Limit
Compliance Status
pH 5.52 – 7.26 (6.50 ±
0.42)
6.5 – 8.0 6.5 – 8.5 Acceptable (slightly
acidic)
Temperature
(°C)
51.4 – 74.3 (63.2 ±
7.2)
NS NS Typical geothermal
EC (µS/cm) 5.16 – 51.22 (19.47 ±
7.5)
1000 1200 Low mineralization
TDS (ppm) 2.58 – 25.6 (10.2 ±
3.4)
1000 1200 Excellent quality
As (ppb) 2.24 – 5.49 (3.86 ±
1.05)
10 10 Below limits
Pb (ppb) 0.95 – 1.98 (1.43 ±
0.31)
10 50 Below limits
Cd (ppb) 0.39 – 1.41 (0.84 ±
0.34)
3 10 Below limits
Hg (ppb) ND 5 1 Not detected
Note: ND = Not Detected; NS = Not Specified.
Health Risk Assessment
Non-Carcinogenic Health Risk
Hazard Quotient (HQ) and cumulative Hazard Index (HI) values were computed for adults and children to
quantify potential non-carcinogenic risks from exposure to heavy metals through ingestion of fumarolic
condensates, following the U.S. Environmental Protection Agency (USEPA, 2011) guidelines. Similar
approaches have recently been applied in heavy-metal risk assessments for water resources using probabilistic
and deterministic exposure models (Ayaz et al., 2023; Shetty et al., 2024).
All HQ values for adults remained below unity (As = 0.32 ± 0.12; Pb = 0.02 ± 0.01; Cd = 0.02 ± 0.01), yielding
a cumulative HI = 0.36. These values indicate a negligible likelihood of non-cancer health effects arising from
short- or long-term exposure to the condensates. In contrast, HQ values for children were comparatively higher,
particularly for arsenic (mean = 0.68 ± 0.20), producing a cumulative HI = 0.80, which approaches the critical
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threshold of 1. This pattern, also reported in recent global health-risk studies (Ayaz et al., 2023; Shetty et al.,
2024), reflects children’s greater vulnerability to contaminant exposure due to their higher water-intake rates and
lower body weights. Elevated HQ values in the inner-caldera fumaroles (F9 and F10) imply that children living
near these high-temperature vents may experience marginal but notable health risks associated with geothermal
trace-metal exposure.
The heightened vulnerability of children stems from their lower body weight combined with a relatively greater
ingestion rate per kilogram, leading to proportionally higher internal exposure to trace metals—this pattern has
been emphasized in studies of contaminant exposure in pediatric populations (Bair, 2022; Capitão et al., 2022).
Spatially, the non-carcinogenic risk indices (HQ and HI) track closely with the gradient in metal concentrations,
increasing toward hotter inner-caldera vents. Although all values remain below the safety threshold, this radial
trend suggests a temperature-controlled mobilization of metals and highlights zones of localized exposure risk
that merit periodic surveillance (Shetty et al., 2024).
The comparative plots in Figure 2 clearly demonstrate age-related differences in susceptibility to metal exposure
from fumarolic condensates. In both Hazard Quotient (HQ) and Lifetime Cancer Risk (LCR) profiles, children
consistently exhibit higher values than adults, reflecting their enhanced physiological vulnerability to geogenic
contaminants. This disparity arises primarily from children’s lower body weight, higher ingestion rate per unit
body mass, and immature detoxification mechanisms, which collectively amplify internal doses even at
comparable environmental concentrations (Jadoon et al., 2025; Okoro et al., 2025). Similar findings have been
reported in recent exposure-risk studies, where non-carcinogenic and carcinogenic indices for As, Pb, and Cd
were substantially higher in children than in adults consuming contaminated groundwater resources,
underscoring the importance of age-specific risk evaluation and protective public health interventions (Gantayat
et al., 2025).
Fig 2: Comparative Non-Carcinogenic (HQ) and Carcinogenic (LCR) Risks for Adults and Children across
Fumarolic Vents
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The upper panel of Figure 2 shows that HQ values for adults ranged between 0.15 and 0.50 across fumaroles, all
below the USEPA (2011) threshold of 1, implying negligible non-cancer health risks. In contrast, HQ values for
children vary from 0.30 to 0.98, approaching the critical limit at fumaroles F9 and F10. These vents correspond
to the inner caldera, where elevated temperatures (>73 °C) and vigorous vapor flux enhance rock–steam
interactions, thereby promoting the leaching and volatilization of arsenic and cadmium from hydrothermally
altered rocks. Similar processes have been reported in other geothermal fields, where higher vent temperatures
and vapor-dominated systems accelerate trace-metal mobilization into condensates (Durowoju et al., 2020;
Fahimah et al., 2024).
The spatial trend indicates a progressive increase in HQ from peripheral vents (F1–F6) toward the inner caldera
(F8–F10). This pattern mirrors the geothermal intensity gradient and confirms that elevated fumarolic
temperatures amplify heavy-metal transfer into vapor condensates, as observed in comparable high-enthalpy
geothermal environments (Durowoju et al., 2020). The mean HQ and cumulative HI values—0.36 for adults and
0.80 for children—further reaffirm that although current exposure levels remain within acceptable limits,
children residing near hot vents face marginal, but notable non-carcinogenic risks associated with geogenic
arsenic and cadmium emissions.
Carcinogenic Health Risk
Lifetime Cancer Risk (LCR) values were computed for arsenic and cadmium using USEPA (2011) slope factors
of 1.5 and 6.3 (mg kg⁻¹ day⁻¹)⁻¹, respectively. For adults, total LCR ranged between 4.1 × 10⁻⁵ and 2.1 × 10⁻⁴
(mean = 7.6 × 10⁻⁵), while for children, it varied from 1.9 × 10⁻⁵ to 9.8 × 10⁻⁵ (mean = 1.8 × 10⁻⁴). These values
fall within or slightly above the USEPA’s acceptable range (10⁻⁶–10⁻⁴), consistent with recent studies reporting
similar risk magnitudes for waterborne arsenic and cadmium exposure in geothermal and hydrothermal
environments (Saber et al., 2024).
The highest LCR values were observed in fumaroles F9 and F10 (inner caldera), where elevated temperatures
(> 73 °C) and strong vapor discharge likely enhance volatilization and partitioning of arsenic and cadmium into
condensate fluids. Processes of temperature-driven leaching and magmatic fluid input have been shown in
geothermal systems to elevate trace-metal burdens in high-temp fluids (Saby et al., 2024)
The highest LCR values were observed at fumaroles F9 and F10 (inner caldera), where elevated temperatures (>
73 °C) and intense vapor discharge likely enhance the volatilization and partitioning of arsenic and cadmium
into condensate. This aligns with findings from geothermal settings demonstrating that high-temperature zones
promote trace-metal mobilization and gas–water exchange (Taufiq, 2023).
CONCLUSION
The study establishes that fumarolic condensates from the Mt. Suswa geothermal field exhibit low to moderate
heavy-metal enrichment largely controlled by geothermal intensity and rock–steam interactions. The
concentrations of arsenic (2.24–5.49 ppb), lead (0.95–1.98 ppb), and cadmium (0.39–1.41 ppb) were well below
the WHO (2022) and NEMA (2024) limits for potable water, confirming the condensates’ acceptable chemical
quality.
Spatial variability indicates that vents within the inner caldera (F9–F10) recorded the highest As and Cd
concentrations, corresponding to zones of elevated temperature and vapor flux that enhance metal volatilization
from hydrothermally altered rocks.
Health-risk assessment revealed that non-carcinogenic risks (HQ < 1) are negligible for adults and marginal for
children, while carcinogenic risks (LCR ≈ 10⁻⁵–10⁻⁴) remain within or slightly above the USEPA acceptable
range. Generally, fumarolic condensates from Mt. Suswa are safe for limited domestic use but require periodic
monitoring and local mitigation such as point-of-use treatment (bone char or activated alumina) and community
awareness to minimize exposure in high-temperature vent areas.
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ACKNOWLEDGMENTS
The author expresses sincere gratitude to Prof. Kitetu Kitetu and Dr. Carolyne Chepkirui of Kabarak University
School of Science, Engineering and Technology for their invaluable contribution throughout this research. The
cooperation of the Mt. Suswa local community during field sampling is deeply acknowledged.
Conflict of Interest
The authors affirm their complete impartiality, declaring that no conflicts of interest exist, thereby reinforcing
the credibility, transparency, and integrity of the research findings.
Ethical Approval
Ethical approval for this study was obtained from the Kabarak University Ethics Review Committee (KUERC)
in accordance with national research ethics guidelines. The approval covered both environmental sampling and
the administration of household surveys involving human participants. Research authorization was subsequently
granted by the National Commission for Science, Technology and Innovation (NACOSTI) under license number
NACOSTI/P/25/4176440, permitting fieldwork within the Mt. Suswastudy area.
Data Availability
The datasets generated and analyzed during this study (physico-chemical parameters, heavy-metal
concentrations, HQ/HI/LCR indices, and geospatial coordinates) are available from the corresponding author
upon reasonable request.
Supplementary materials, analytical calibration curves, and raw instrumental data have been archived with the
Kabarak University Institutional Repository for academic reference.
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