Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

Association between the alga Spirogyra (Zygnemataceae) and heavy metals

in sediments of the Chi River Basin in Northeast Thailand

Patarapong Kroeksakul1*; https://orcid.org/0000-0003-3201-8996

Arin Ngamniyom1; https://orcid.org/0000-0002-2325-0622

Phanom Sutthisaksopon1; https://orcid.org/0009-0009-2609-2015

Pakjirat Singhaboot2; https://orcid.org/0009-0003-4698-5482

1. Faculty of Environmental Culture and Ecotourism, Srinakharinwirot University, Ongkharak, Nakhon Nayok,

Thailand. 26120; patarapong@g.swu.ac.th (*Correspondence), arin@g.swu.ac.th, phanom@g.swu.ac.th

2. Faculty of Agricultural Product Innovation and Technology, Srinakharinwirot University, Ongkharak, Nakhon Nayok,

Thailand. 26120; pakjirat@g.swu.ac.th

Received 04-VII-2025. Corrected 11-IX-2025. Accepted 22-XI-2025.

ABSTRACT

Introduction: Sediments act as major sinks of heavy metals from human activities, while algae such as Spirogyra

interact with these sediments through nutrient uptake and biogeochemical cycling. In the Chi River Basin,

Spirogyra (“Tao”) plays both ecological and socioeconomic roles, serving as food and a bioindicator of pollution.

Objective: To evaluate heavy-metal concentrations in sediments and Spirogyra and assesses their potential

human health risks.

Methods: Water quality, Spirogyra, and sediment samples from the Chi River Basin were analyzed for heavy met-

als using ICP-OES, with human health risks assessed by THQ and HI, and sediment contamination evaluated

through Igeo, EF, CF, PLI indices.

Results: Heavy metals (Cd, Cu, Fe, Mn, Zn) in sediments and Spirogyra from the Chi River Basin were assessed

under average water conditions (pH 7.49, EC 497 µS cm–2, NaCl 0.024 %, 24.9 ± 3.52 °C), showing concentrations

in algae (Fe > Mn > Zn > Cu > Cd) with THQ and HI < 1 indicating low health risk, while sediments (Mn > Fe >

Zn > Cu > Cd) exhibited Igeo < 0, EF < 2, CF < 1 except for Fe (CF = 8.31), PLI < 1, and significant correlations

between Mn in algae with Cu and Mn in sediments, Cu with Fe in algae, and Cd in algae with Fe in sediments.

Conclusions: The findings indicate no significant heavy-metal pollution in sediments or Spirogyra from the Chi

River Basin. However, due to elevated Fe contamination in sediments, periodic monitoring is recommended to

safeguard ecological and food safety.

Key words: Spirogyra; sediment; heavy metals; Chi River Basin.

RESUMEN

Asociación entre el alga Spirogyra (Zygnemataceae) y metales pesados en sedimentos

de la cuenca del río Chi en el noreste de Tailandia

Introducción: Los sedimentos actúan como sumideros principales de metales pesados provenientes de activi-

dades humanas, mientras que algas como Spirogyra interactúan con estos sedimentos a través de la absorción de

nutrientes y el ciclo biogeoquímico. En la cuenca del río Chi, Spirogyra (“Tao”) cumple funciones tanto ecológicas

como socioeconómicas, sirviendo como alimento y bioindicador de contaminación.

https://doi.org/10.15517/x61ae455

AQUATIC ECOLOGY

2Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

INTRODUCTION

Sediments in water bodies contain the

bulk of the heavy metals (HMs) produced by

human activities (Guan et al., 2018; Liber et al.,

2019; Sojka & Jaskuła, 2022). Fluvial processes

(Foster & Charlesworth, 1996; Miller, 1997;

Rahman et al., 2022; Schulte et al., 2024) and

the decomposition of algae are involved in the

biogeochemical cycles of HMs in the sediment

(Ni et al., 2019; Wang et al., 2023; Xue et al.,

2024). A variety of species, including algae, use

silt as a source of nutrients (Park & Hwang,

2010; Xiang et al., 2023; Zhao et al., 2022), and

thus may influence such cycles by removing

HMs from the sediment (Machado et al., 2024;

Sarma et al., 2024; Zada et al., 2021).

Algae are a diverse group of photosynthetic

eukaryotes (Friedl et al., 2011; Kaštovsky et

al., 2019) that have multiple uses, including as

alternative energy sources (Hannon et al., 2010;

Mohite et al., 2024; Neeti et al., 2023), in water

treatment (Abdel-Raouf et al., 2012; Bhatt et

al., 2022; Molinuevo-Salces et al., 2019), and in

industry, especially in food production such as

Undaria pinnatifida, Wolffia globosa, Spirogyra

etc., (Matos et al., 2022; Naik et al., 2024). Algae

are high in protein, vitamins, lipids, minerals,

and essential fatty acids (de Oliveira & Bragot-

to, 2022; Kent et al., 2015; Wu et al., 2023).

The people inhabiting the Chi River Basin

use algae of the genus Spirogyra (Phylum Chlo-

rophyta, Family Spirogyraceae), known locally

as Tao, as a commodity. Spirogyra can also be

used as a bioindicator of pollution, including

the HMs that can contaminate the water and

sediments in reservoirs (Rajfur et al., 2010;

Shing et al., 2018; Wijaya et al., 2025). The

analysis of pertinent elements in ecosystems

(Ewing & Weathers, 2021; Lobus & Kulikovs-

kiy, 2023; Spohn et al., 2021) includes the

interactions between HMs in sediments and

algae. Understanding these relationships in

ecosystems allows for better environmental

management. In this study, we aimed to assess

the hazards to human health posed by specific

HMs in the sediments and Spirogyra of the Chi

River basin in Thailand.

MATERIAL AND METHODS

Water conditions and study sites: The

basic data characterizing the aquatic environ-

ments at the study sites are provided in Table 1.

The pH, electrical conductivity, percentage of

sodium chloride (NaCl) in the water, and the

water temperature were measured, and the

sample locations were recorded as Universal

Transverse Mercator (UTM) coordinates. Fig. 1

shows the area of the river basin. The types of

Objetivo: Evaluar las concentraciones de metales pesados en sedimentos y Spirogyra, y analiza sus posibles riesgos

para la salud humana.

Métodos: Se analizaron la calidad del agua, Spirogyra y sedimentos de la cuenca del río Chi para detectar metales

pesados mediante ICP-OES; los riesgos para la salud humana se evaluaron mediante THQ y HI, y la contamina-

ción de los sedimentos se determinó con los índices Igeo, EF, CF y PLI.

Resultados: Los metales pesados (Cd, Cu, Fe, Mn, Zn) en sedimentos y Spirogyra de la cuenca del río Chi fueron

evaluados bajo condiciones promedio del agua (pH 7.49, CE 497 µS cm-2, NaCl 0.024 %, 24.9 ± 3.52 °C), mos-

trando concentraciones en algas (Fe > Mn > Zn > Cu > Cd) con THQ y HI < 1 que indican bajo riesgo para la

salud, mientras que los sedimentos (Mn > Fe > Zn > Cu > Cd) presentaron Igeo < 0, EF < 2, CF < 1 excepto para

Fe (CF = 8.31), PLI < 1, y correlaciones significativas entre Mn en algas con Cu y Mn en sedimentos, Cu con Fe

en algas, y Cd en algas con Fe en sedimentos.

Conclusiones: Los resultados indican que no existe una contaminación significativa por metales pesados en los

sedimentos ni en Spirogyra de la cuenca del río Chi. Sin embargo, debido a la elevada contaminación por Fe en los

sedimentos, se recomienda un monitoreo periódico para proteger la seguridad ecológica y alimentaria.

Palabras clave: Spirogyra; sedimento; metales pesados; Cuenca del río Chi

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

water bodies the Spirogyra samples were col-

lected from are listed in Table 1. However, the

environmental conditions, including pH, elec-

trical conductivity (EC), and salinity, influence

the accumulation of toxins by altering their

chemical properties and bioavailability to liv-

ing organisms. They also influence the health

and functionality of living organisms regarding

toxin buildup.

Spirogyra collection: The Spirogyra sam-

ples were scooped from the water by hand,

after which they were cleaned with pure water,

packed in plastic zipper bags, and kept at -4

°C before being sent to the laboratory. In the

laboratory, the alga were air-dried for five h,

then dried at 60 °C in a hot oven for 120 h. The

water content of the Spirogyra was calculated

to have been around 91.9 ± 0.730 %. The dried

samples were ground and sifted through a No.

20 sieve, then collected in polyethylene tubes

before being maintained in the refrigerator at a

temperature of 4 °C.

Algal extraction and analysis of heavy

metals: The algae were prepared for extraction

Fig. 1. Sample Locations in the Chi River Basin.

Table 1

Water characteristics and types of water bodies at the study sites.

Location Water Characteristics Coordinates (UTM) Water B o dy

pH EC (µS cm–2)% NaCl Temperature Northing Easting Zone

1 7.97 495 0.05 27.3 °C 809847 1727556 47P Lake

2 7.67 194 0 23.7 °C 818007 1836476 47Q Canal

3 7.4 525 0.02 29.5 °C 267554 1805080 48Q Paddy Field

4 7.78 1.083 0.05 19.1 °C 290743 1809612 48Q Lake

5 6.66 188 0 25.2 °C 422056 1714464 48P Canal

Average 7.49 497 0.024 24.9 °C –– –– –– ––

SD 0.456 326 0.022 3.52 –– –– –– ––

Note: EC = electrical conductivity; % NaCl = percentage of sodium chloride (NaCl) in water soluble; SD = standard deviation.

4Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

by mixing 0.1 mol l–1 of nitric acid (HNO3) and

0.1 mol l–1 of sodium hydroxide (NaOH) in a 50

ml volume with 1 g of sample in 100 ml conical

flasks. The flasks were agitated at 200 rpm for 6

h (Mehta & Gaur, 2005; Sheng et al., 2004). The

solution was then filtered. The HM analysis

was performed on the residue using inductively

coupled plasma atomic emission spectroscopy

(ICP-OEM) (PlasmaQuant 9100 series, Germa-

ny). Quality assurance and quality control pro-

cedures were performed on all 20 samples, as

well as the duplicates and blanks. The samples

were compared against multi-element standard

solutions from AccuStandard (USA).

Algae and health risk indicators: From

the algal samples, the target hazard quotient

(THQ) and hazard index (HI) (or sum of the

THQs) (Guerra et al., 2012; Javed & Usamni,

2016; Thummajitsakul et al., 2018) were calcu-

lated to assess the risk to human health. A THQ

of < 1 indicates little chance of the exposed per-

son experiencing any adverse effects. The THQ

was calculated as follows:

(1)

where EF is the exposure frequency from the

consumption of HMs in vegetables (365 days

year–1), with the assumption that the Spiro-

gyra is being eaten in the same way as fresh

vegetables; ED is the exposure duration during

the average lifetime of a Thai citizen (i.e., 75.2

years for adult males and 81.3 years for adult

females) (Thailand Board of Investment, 2025);

FIR is the food ingestion rate of a Thai citizen,

equal to 0.268 kg person–1 day–1 for adult males

and 0.283 kg person–1 day–1 for adult females

(Thummajitsakul et al., 2018); C is the quantity

of HMs in the algae (mg kg–1); RFD is the oral

references dose, which is 0.001 mg kg–1 day–1

for cadmium (Cd), 0.04 mg kg–1 day–1 for cop-

per (Cu), 0.7 mg kg–1 day–1 for iron (Fe), 0.14

mg kg–1 day–1 for manganese (Mn), and 0.3

mg kg–1 day–1 for zinc (Zn) (Thummajitsakul

et al., 2018; U.S. Environmental Protection

Agency, 1988); WAB is the average body weight

of a Thai citizen (68.83 kg for adult males and

57.4 kg for adult females) (Thummajitsakul et

al., 2018); and TA is the average exposure time

for HMs (ED × 365 days year–1).

The HI was used to estimate the overall

potential health risk from more than one HM,

based on the following:

HI = THQCd + THQCu + THQFe + THQMn + THQZn (2)

where HI < 1 indicates no significant health

risk.

Sediment collection and extraction:

Approximately 5 kg of sediment was collected

at each site, placed in plastic bags, and kept in

a box for transport from the field to the labora-

tory, where the sediment was dried at 105 °C in

a hot oven for 120 h, after which it was ground

using a mortar and pestle. After being passed

through a No. 4 (10 mm) sieve, the sediment

was extracted for use in ICP-OES analysis. For

this, 2 g of each prepared soil sample was mixed

with concentrated hydrofluoric acid (HF), con-

centrated perchloric acid (HClO4), and con-

centrated HNO3 at a ratio of 1 : 1 : 1 for a total

volume of 20 ml. Extraction was performed

at 500 °C in a SpeedDigester K-425 BUCHI

instrument (Switzerland). Each residue was

rinsed with 1 % HNO3 and passed through filter

paper. The supernatant was transferred to a 50

ml volumetric flask, and 1 % HNO3 was added

for continued ICP-OES analysis (PlasmaQuant

9100 series, Germany). The quality assurance

and quality control procedures ensured that all

20 samples, as well as duplicates and blanks,

were collected, processed, and examined to

standard. The samples were compared against

ICP-OEM multi-element standard solutions

(AccuStandard, USA).

Sediment indicators: The quality of the

sediment was assessed by several indicators:

the geo-accumulation index (Igeo), the enrich-

ment factor (EF), and the contamination factor

(CF). The Igeo was originally formulated by

Muller (1980) and is a quantitative measure of

pollution in aquatic sediments (Kroeksakul et

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

al., 2023; Nobi et al., 2010), developed through

an understanding of the lithogenic effect, and

calculated using the following formula:

Igeo = log2 [Cn / 1.5Bn] (3)

where Cn is the measured concentration of an

element in the sediment; and Bn is the back-

ground value of the element. The interpreted

values of Igeo are: < 0 = not polluted; 0-1 = not

polluted to moderately polluted; 1-2 = mod-

erately polluted; 2-3 = moderately to strongly

polluted; 3-4 = strongly polluted; 4-5 = strongly

to extremely polluted, and > 5 = extremely

polluted.

The EF was calculated in the following

way:

EF = (C / RE) sample / (C / RE) background (4)

where (C/RE) sample (background) is the

concentration (C) of an element compared

to a reference element (RE) in the sample

(background). Aluminum (Al) was used as the

reference element because it is a major compo-

nent of clay. The interpreted values of the EF

are: < 2 = deficiency in mineral enrichment;

2-5 = moderate enrichment; 5-20 = significant

enrichment; 20-40 = very high enrichment; and

> 40 = extremely high enrichment.

The CF was approximated as the observed

concentration of an element in the sample (Ci)

to the background level of the same element

(Cb), as follows:

CF = Ci / Cb (5)

The interpreted values of the CF are: < 1 =

low pollution level; 1-3 = moderate pollution

level; 3-6 = considerable pollution level; and >

6 = very high pollution level. The background

element values for the Igeo, EF, and CF calcula-

tions were taken from reference data for Al,

Cu, Fe, and Zn in Potipat et al. (2015). The Cd

background references were obtained from the

Land Development Department (2012), and

the Mn background references were from Czar-

nowska and Gworek (1990). The CFs were used

to calculate the pollution load index (PLI) that

was used to measure the general contamination

level, as follows:

PLI = x CF2 x CF3….CFn (6)

where n is the number of observed elements.

The interpreted values of the PLI are: 0 =

unpolluted; < 1 = baseline level for no pollu-

tion; and > 1 = polluted.

Statistical analysis: The data were analyzed

using one-way analysis of variance, and the dif-

ferences between datasets were compared using

a least significant difference (LSD) test with p <

0.05. The correlations were assessed using Pear-

son’s correlation coefficient (r). All analyses

were conducted using Statistical Package for the

Social Sciences (SPSS) v.22 software.

RESULTS

Heavy metal content in Spirogyra: The

HM contents determined in the Spirogyra sam-

ples are listed in Table 2. The Cd and Cu con-

tents in the algae from Site 5 were significantly

greater than those from Sites 1, 2, and 3 (p <

0.05), and the Fe content in the algae from Site

5 was significantly greater than at Sites 1, 2, and

3 (p < 0.05). The Mn content in the algae from

Site 5 was less than at Sites 1 and 2, and the

Zn content in algae. The HM contents in the

Spirogyra samples were mostly Fe (about 80 %)

(Fig. 2).

Human health risk assessment: The peo-

ple of the Chi River Basin use Spirogyra to

make a salad the locals call “Laab Tao”, and this

may become useful as a food resource in the

future. The THQs occurred in the order Mn

> Fe > Cu > Zn > Cd for males and Cu > Fe >

Mn > Zn > Cd for females (Table 3). The THQ

values were < 1, and the HI value for the adult

males averaged 5.490 ± 1.512 x 10–4 higher than

the adult female average of 122 ± 63.9 x 10–4.

The HI values for the adult males and females

were both < 1, indicating no significant risk to

human health.

6Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

Heavy metals in the sediments: In the

sediment samples, Cd averaged 0.005 ± 0.000

mg kg-1 dry weight, and the amount from Site

2 (0.004 ± 0.000 mg kg-1) was significantly less

(p < 0.05) than at Sites 1, 3, 4, and 5. The Cu

content from Site 4 averaged 0.713 ± 0.026 mg

kg-1, which was significantly less (p < 0.05)

than at Sites 1 and 2. At all sites, the Fe and

Mn contents were both significant (p < 0.05).

The Zn content at Site 3 averaged 36.0 ± 16.0

mg kg–1 and was significantly higher (p < 0.05)

than at the other sites. The HM contents in the

sediments are presented in Table 4 and illus-

trated in Fig. 3. The Mn content was about 59

% of the total HMs in the sediments, and Fe was

the most abundant HM in the algae (Fig. 3F).

Fig. 2. The HM content in Spirogyra by site. A. Cd, B. Cu, C. Fe, D. Mn, E. Zn, F. Percentage of five HMs in Spirogyra.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

Table 2

Heavy metal contents in Spirogyra in the Chi River Basin.

Location Heavy Metal Dry Weight in Spirogyra (mg kg–1)

Cd Cu Fe Mn Zn

Site 1 0.030(± 0.039)a0.626(± 0.015)a175(± 6.91)a207(± 21.1)a6.09(± 0.263)a

Site 2 0.007(± 0.000)a1.09(± 0.981)a37.2(± 49.4)a222(± 160)a11.6(± 11.0)a

Site 3 0.007(± 0.000)a0.670(± 0.538)a326(± 546)a86.9(± 43.3)ab 2.63(± 1.58)a

Site 4 0.007(± 0.000)a1.65(± 0.842)ab 900(± 6.91)ab 55.7(± 5.52)b8.97(± 0.539)a

Site 5 0.007(± 0.000)a3.13(± 1.87)b2.920(± 2.616)b125(± 0.463)ab 11.4(± 0.759)a

Average 0.012(± 0.017) 1.43(± 1.30) 872(± 1541) 139(± 92.9) 8.13(± 5.50)

Note: a, b Difference is significant at p < 0.05 (LSD); Cd = cadmium; Cu = copper; Fe = iron; Mn = manganese; Zn = zinc.

Table 3

THQs and HIs for Spirogyra as a measure of heavy metals contamination in male and female adults (Aged over 15 years).

Location THQ (mean ± SD) HI

(mean ± SD) (x 10–4)*

Cd (x 10–4)* Cu (x 10–4)* Fe (x 10–4)* Mn (x 10–4)* Zn (x 10–4)*

Male

Site1 1.20(± 1.27) 0.61(± 0.01) 9.79(± 0.31) 8.095(± 673) 0.79(± 0.03) 8.108(± 672)

Site2 0.29(± 0.01) 1.06(± 0.78) 2.07(± 2.25) 8.644(± 5.095) 1.51(± 1.17) 8.649(± 5,099)

Site3 0.30(± 0.00) 0.65(± 0.43) 18.1(± 24.8) 3.385(± 1.473) 0.34(± 0.17) 3.405(± 1,499)

Site4 0.29(± 0.00) 1.61(± 0.67) 50.0(± 44.5) 2.169(± 175) 1.16(± 0.06) 2.222(± 167)

Site5 0.28(± 0.01) 3.05(± 1.49) 162(± 118) 4.900(± 14.7) 1.48(± 0.08) 5.067(± 123)

Average 0.47(± 0.26) 1.40(± 0.68) 48.5(± 38.1) 5.438(± 1,486) 1.06(± 0.30) 5.490(± 1,512)

Female

Site1 1.51(± 1.61) 12.39(± 0.40) 73.2(± 6.09) 7.51(± 0.26) 1.00(± 0.04) 95.6(± 4.48)

Site2 0.37(± 0.01) 2.62(± 2.84) 78.1(± 46.0) 14.3(± 11.1) 1.91(± 1.48) 97.3(± 61.5)

Site3 0.38(± 0.00) 23.0(± 31.4) 30.6(± 13.3) 3.24(± 1.60) 0.43(± 0.21) 57.7(± 46.2)

Site4 0.37(± 0.00) 63.4(± 56.4) 19.6(± 1.59) 11.0(± 0.54) 1.47(± 0.07) 95.9(± 56.1)

Site5 0.36(± 0.01) 205(± 150) 44.3(± 0.13) 14.0(± 0.76) 1.87(± 0.10) 266(± 151)

Average 0.60(± 0.33) 61.4(± 48.3) 49.1(± 13.4) 10.0(± 2.86) 1.34(± 0.38) 122(± 63.9)

Note: *x 10–4 means the value in the table must be divided by 10 000 to obtain the actual value; Cd = cadmium; Cu = copper;

Fe = iron; Mn = manganese; Zn = zinc.

Table 4

Heavy metal contamination in the sediment by study site.

Location Heavy metal dry weight in sediment (mg kg-1)

Cd Cu Fe Mn Zn

Site1 0.005(± 0.000)a2.07(± 0.228)a725(± 23.6)a857(± 30.5)a5.64(± 0.114)a

Site2 0.004(± 0.000)b2.72(± 1.07)a260(± 22.5)b920(± 27.0)b6.51(± 1.03)a

Site3 0.005(± 0.000)ac 1.41(± 0.029)ab 47.2(± 7.94)c37.7(± 1.23)c36.0(± 16.0)b

Site4 0.005(± 0.000)ac 0.713(± 0.026)b211(± 10.1)d208(± 13.8)d3.21(± 0.356)a

Site5 0.005(± 0.000)c1.52(± 0.052)ab 164(± 26.8)e90.6(± 10.9)e5.37(± 0.103)a

Average 0.005(± 0.000) 1.68(± 0.811) 281(± 241) 422(± 398) 11.3(± 14.2)

Note: a, b, c, d, e Difference is significant at p < 0.05 (LSD); Cd = cadmium; Cu = copper; Fe = iron; Mn = manganese; Zn = zinc.

8Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

Sediment quality analysis: The Igeo values

for Cu and Fe in the sediments from all sites

were < 0, indicating no significant pollution.

The Mn from Sites 1 and 2 had values > 0, indi-

cating moderately polluted, with Sites 3, 4, and

5 being < 0. The Zn at all sites had Igeo < 0. The

ranking of the mean Igeo values was in the order

Mn > Zn > Cu > Fe > Cd. The statistics for the

comparisons between sites and Igeo values are

listed in Table 5 and shown in Fig. 4. The EF

values were < 1, indicating no enrichment or

a minimal effect from human activities. The

mean EF values were in the order Mn > Zn >

FE > Cu > Cd. The statistics for the sites and EF

values are presented in Table 5 and Fig. 4. The

CF values for Cd, Cu, Mn, and Zn were < 1,

Fig. 3. Heavy metal content in the sediment by Site. A. Cd, B. Cu, C. Fe, D. Mn, E. Zn, F. Percentages of five HMs in Spirogyra.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

indicating low pollution levels, although the

CF value of Fe (8.31 ± 7.12) indicates a very

high pollution level. The PLI values at each site

were < 1, indicating no significant pollution

in the Spirogyra habitat in the Chi River basin

(Table 6).

Relationship between heavy metal con-

tents in Spirogyra and sediments: The rela-

tionship between the HMs in the Spirogyra and

sediment samples was evaluated using Pearson’s

r. There were positive correlations between Cd

in the algae and Fe in the sediment (r = 0.530,

p < 0.05), between Mn in the algae and Cu in

the sediment (r = 0.920, p < 0.01), Mn in the

algae and Mn in the sediment (r = 0.669, p <

0.01), and Zn in the algae and Mn in the sedi-

ment (r = 0.920, p < 0.01). There was a negative

correlation between Mn in the algae and Cd in

the sediment (r = -0.530, p < 0.05). The cor-

relations among the other HMs are presented

in Table 7.

Factor analysis of heavy metal contents

in Spirogyra and sediments: The HMs were

used as parameters in a principal component

analysis (PCA). Prior to the analysis, the HM

contents of the Spirogyra and sediment sam-

ples were tested using the Kaiser-Meyer-Olkin

(KMO) and Bartlett tests. The KMO measure

of sampling adequacy was 0.419, and there was

a significant difference between the eigenval-

ues (p < 0.001) (Table 8). The PCA identified

three principal components (PCs) with eigen-

values > 1.5 that collectively explained 80.3 %

of the total variance in the dataset (Table 9 and

Table 5

Heavy metal contamination of Spirogyra reservoir habitats in the Chi River basin.

Indicator HM

Cd Cu Fe Mn Zn

Igeo

Site1 -9.06(± 0.002)a-4.62(± 0.164)ad -6.48(± 0.047)a0.827(± 0.051)a-5.40(± 0.029)a

Site2 -9.19(± 0.014)b-4.29(± 0.526)a-7.97(± 0.127)b0.929(± 0.042)a-5.20(± 0.239)a

Site3 -9.06(± 0.003)ac -5.16(± 0.029)b-10.4(± 0.242)c-3.67(± 0.046)b-2.83(± 0.721)b

Site4 -9.05(± 0.002)ac -6.15(± 0.053)c-8.26(± 0.068)b-1.21(± 0.095)c-6.21(± 0.163)c

Site5 -9.04(± 0.003)c-5.06(± 0.050)d-8.64(± 0.239)d-2.42(± 0.169)d-5.47(± 0.027)a

Average -9.08(± 0.056) -5.05(± 0.687) -8.36(± 1.32) -1.11(± 1.86) -5.02(± 1.22)

Site1 0.002(± 0.000)a0.061(± 0.006)ab 0.016(± 0.000)a0.266(± 0.009)a0.035(± 0.000)a

Site2 0.002(± 0.000)b0.080(± 0.031)a0.005(± 0.000)b0.285(± 0.008)b0.040(± 0.006)a

Site3 0.002(± 0.000)ac 0.041(± 0.000)bc 0.001(± 0.000)c0.011(± 0.000)c0.226(± 0.100)b

Site4 0.002(± 0.000)ac 0.021(± 0.000)c0.004(± 0.000)d0.064(± 0.004)d0.020(± 0.002)a

Site5 0.002(± 0.000)c0.044(± 0.001)bc 0.003(± 0.000)e0.028(± 0.003)e0.033(± 0.000)a

Average 0.002(± 0.000) 0.049(± 0.023) 0.06(± 0.005) 0.131(± 0.123) 0.071(± 0.089)

Site1 0.000(± 0.000)a1.22(± 0.134)ac 21.3(± 0.697)a0.266(± 0.009)a0.035(± 0.000)a

Site2 0.000(± 0.000)b1.60(± 0.629)a7.67(± 0.664)b0.285(± 0.008)b0.040(± 0.006)a

Site3 0.000(± 0.000)a0.834(± 0.017)bc 1.39(± 0.234)c0.011(± 0.000)c0.226(± 0.100)b

Site4 0.000(± 0.000)ac 0.419(± 0.015)b6.24(± 0.298)d0.064(± 0.004)d0.020(± 0.002)a

Site5 0.000(± 0.000)c0.894(± 0.030)c4.85(± 0.791)e0.028(± 0.003)e0.033(± 0.000)a

Average 0.000(± 0.000) 0.994(± 0.477) 8.31(± 7.12) 0.131(± 0.123) 0.071(± 0.089)

Note: a, b, c, d, e Difference significant at p < 0.05 (LSD); Igeo = Geo-Accumulation index; EF = Enrichment Factor; CF =

Contamination Factor; Cd = cadmium; Cu = copper; Fe = iron; Mn = manganese; Zn = zinc.

10 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

Fig. 4. Sediment quality in the reservoir habitat of Spirogyra in the Chi River basin. A. Igeo, B. EF, C. CF.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

Fig. 5A), with each of the three components

explaining > 10 % of the variance. The most

important contributors to PC1 were Mn in the

algae (0.878), Cu in the sediment (0.927), and

Mn in the sediment (0.714). This group is indi-

cated by the red ellipse in Fig. 5B. For PC2, the

factor loading of Cu of the algae was 0.976 and

Fe in the algae was 0.882. This group appears in

the green ellipse in Fig. 5B. For PC3, the factor

loading of Cd in the algae was 0.734 and Fe in

the sediment was 0.907. This group is shown in

the yellow ellipse in Fig. 5B.

DISCUSSION

This study found that the measured heavy

metal levels in Spirogyra were below Thailand’s

food safety standards, which stipulate that cad-

mium concentrations in dried seaweed must

not surpass 2 mg kg-¹, and the test results con-

firmed compliance with these standards.

According to the Pollution Control Depart-

ment’s criteria (2022), the concentration of

heavy metals in sediments does not surpass the

critical contamination thresholds for freshwater

sources, which specify that Cd must be below

Table 7

Correlation between heavy metals contents in the sediment (Soi) and Spirogyra (Al) in the Chi River basin.

 Cd-Al Cu-Al Fe-Al Mn-Al Zn-Al Cd- Soi Cu- Soi Fe- Soi Mn- Soi Zn- Soi

Cd-Al 1 –– –– –– –– –– –– –– –– ––

Cu-Al –– 1 –– –– –– –– –– –– –– ––

Fe-Al –– .935** 1 –– –– –– –– –– –– ––

Mn-Al –– –– –– 1 –– –– –– –– –– ––

Zn-Al –– .568*–– .645** 1 –– –– –– –– ––

Cd- Soi –– –– –– –.530*–– 1 –– –– –– ––

Cu- Soi –– –– –– .920** .520*–.719** 1 –– –– ––

Fe- Soi .530*–– –– –– –– –– –– 1 –– ––

Mn- Soi –– –– –– .669** –– –.687** .706** .728** 1 ––

Zn- Soi –– –– –– –– –– –– –– –– –– 1

Note: * two-tailed p < 0.05; ** two-tailed p < 0.01; Cd-Al = cadmium in algae, Cu-Al = copper in algae, Fe-Al = iron in algae,

Mn-Al = manganese in algae, Zn-Al = zinc in algae, Cd-Soi = cadmium in sediment, Cu-Soi = copper in sediment, Fe-Soi =

iron in sediment, Mn-Soi = manganese in sediment, Zn-Soi = zinc in sediment.

Table 8

Results of the KMO and Bartlett tests on the heavy metal

contents of Spirogyra and the Sediments in the Chi River

basin.

KMO Measure of Sampling Adequacy 0.419

Bartlett’s Test of Sphericity Approximate

Chi Square 177.592

Degrees of Freedom 45

Significance .000

Table 6

PLI values for the sediments from Spirogyra reservoir habitats in the Chi River basin.

Location PLI Meaning

Site1 0.0001169(± 0.00000609)aNo pollution

Site2 0.0000855(± 0.00002124)bNo pollution

Site3 0.0000127(± 0.00000156)cNo pollution

Site4 0.0000139(± 0.00000118)cNo pollution

Site5 0.0000152(± 0.00000196)cNo pollution

Average 0.0000448(± 0.00000641) No pollution

Note: a, b, c, d, e Difference is significant at p < 0.05 (LSD).

12 Revista de Biología Tropical, ISSN: 2215-2075 Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

1 mg kg–1, Cu must be below 31 mg kg–1, and

Zn must be below 120 mg kg–1 (calculated on

a dry weight basis), Fe and Mn are excluded

from the standards due to the significant vari-

ability in their baseline values, which rely on

the sediment source and mineral composition,

rendering a constant control value unattainable.

However, in the natural aquatic ecosystems,

the concentration of heavy metals in sediments

is influenced by both geological factors (parent

material) and anthropogenic activities associ-

ated with the adjacent land use, including agri-

culture, industry, and transportation (Akhtar et

al., 2021; Zha et al., 2024). Consequently, even

though Fe concentrations may be elevated, they

typically do not reach levels that are considered

to be severely polluted when combined with

the Igeo and EF. The accumulation of minerals

from source materials that have been deposited

in sediments for an extended period or from

lithogenic materials within the reservoir may

be the cause of high Fe values (Abdullah et al.,

2020; Fadlillah et al., 2023).

Spirogyra as a possible future food, the

“Future food” is a concept representing food

security and sustainability, referring to the

food’s safety and nutritional value (Çakmakçı

et al., 2024; Galanakis, 2024). The concept

also covers food processing and production.

The dry-weight nutrient content of Spirogyra

includes 12-24 % protein by dry weight, about

43-62 % carbohydrates, and about 15-21 % fats

(Saragih et al., 2019; Sitthiwong, 2019; Yong-

khamcha & Buddhakala, 2023). Regarding the

dietary requirements of minerals, such as Cu,

Fig. 5. Results of the PCA of the heavy metal contents of Spirogyra and the sediments in the Chi River basin. A. Eigenvalues

of the PCA components, B. PC Loadings.

Table 9

Results of the PCA of the heavy metal contents of

Spirogyra and the sediments in the Chi River basin.

PC Component

123

% Variance 39.4 25 15.9

Cumulative % 39.4 64.4 80.3

Eigenvalue 3.93 2.5 1.59

Cd-Alg –0.061 –0.152 0.734

Cu-Alg –0.029 0.976 –0.126

Fe-Alg –0.265 0.882 –0.079

Mn-Alg 0.878 0.116 0.253

Zn-Alg 0.630 0.648 –0.010

Cd-Sed –0.853 0.209 0.132

Cu-Sed 0.927 –0.020 0.158

Fe-Sed 0.215 –0.141 0.907

Mn-Sed 0.714 –0.271 0.562

Zn-Sed –0.169 –0.391 –0.576

Note: PCs = Components; Cd-Al = cadmium in algae;

Cu-Al = copper in algae; Fe-Al = iron in algae; Mn-Al

= manganese in algae; Zn-Al = zinc in algae; Cd-Soi =

cadmium in sediment; Cu-Soi = copper in sediment; Fe-Soi

= iron in sediment; Mn-Soi = manganese in sediment;

Zn-Soi = zinc in sediment.

Revista de Biología Tropical, ISSN: 2215-2075, Vol. 73: e2025219, enero-diciembre 2025 (Publicado Dic. 08, 2025)

Fe, Mn, and Zn, Spirogyra had a Cu content of

1.43 ± 1.30 mg kg-1, with an Fe content averag-

ing 872 ± 1.541 mg kg-1, Mn averaging 139 ±

92.9 mg kg-1, and Zn averaging 18.13 ± 5.50

mg kg-1. Our results indicate that the mineral

content in the Spirogyra is sufficient to meet

recommended daily consumption levels (U.

S. Department of Health and Human Servic-

es, 2025). However, there have been concerns

about the quantity of Cd in the algae associated

with the Fe content in the sediment. We found

that Fe in the sediment averaged 281 ± 241 mg

kg-1 dry weight, and the CF was relatively high

(8.31 ± 7.12), indicating a very high pollution

level. Thus, it will be necessary to monitor the

Cd contents of the algae for consumer safety.

However, the efficacy of each algal species as

bioindicators is contingent upon the environ-

mental and climatic conditions (Anabtawi et

al.,2024; Omar, 2010).

The HM contents in Spirogyra samples

from the Chi River basin occurred in the order

Fe > Mn > Zn > Cu > Cd (85.4 : 13.6 : 0.8 :

0.1 : 0, respectively). The THQ and HI values

for adult males and females indicated no sig-

nificant risks to human health from consuming

the algae. The HM contents in the sediments

occurred in the order Mn > Fe > Zn > Cu > Cd

(58.9 : 39.2 : 1.6 : 0.2:0, respectively). The Igeo

values at all sites were < 0. A deficiency in HM

enrichment was indicated by EF values < 2, and

the CF values for Cd, Cu, Mn, and Zn were <

1, indicating low pollution levels. The CF value

for Fe (mean = 8.31) indicated a high pollution

level, however, especially at Site 1 (21.3), possi-

bly due to human activity around the reservoir.

A PLI value of < 1 indicated no pollution in the

aquatic habitats of Spirogyra in the Chi River

basin. An analysis of the relationships between

the HMs and the algae and the sediments iden-

tified three associations-Mn in the algae and Cu

and Mn in the sediment (PC1), Cu and Fe in

the algae (PC2), and Cd in the algae and Fe in

the sediment (PC3). Spirogyra in the Chi River

Basin is suitable for future food development,

but the Fe content in the sediment should be

monitored because it was positively correlated

with Cd in the algae.

Ethical statement: The authors declare

that they all agree with this publication and

made significant contributions; that there is no

conflict of interest of any kind; and that we fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are fully

and clearly stated in the acknowledgments sec-

tion. A signed document has been filed in the

journal archives.

ACKNOWLEDGMENT

The research was supported by a generous

scholarship from Thailand Science Research

and Innovation (TSRI), transferred to Sri-

nakharinwirot University (Code: 026/2568),

and I would like to thank the Faculty of Envi-

ronmental Culture and Ecotourism for their

analysis tools.

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