Seasonal variation of heavy metals in seagrasses along Thondi coast, Palk Bay, India

Pasumpon & Vasudevan 2021 — Heavy metals in seagrasses, Thondi coast, India

Pasumpon and Vasudevan (2021) measured Mn, Cu, Zn, Pb, Cd, and Cr by atomic absorption spectrophotometry in four live seagrass species (Syringodium isoetifolium, Halodule pinifolia, Cymodocea serrulata, Halophila ovalis) and in dead/decayed offshore seagrass deposition at Thondi coast, Palk Bay, southeast India, across four seasons of 2019–2020. Mn was the most concentrated metal across all species and seasons (peak 15.62 ± 1.02 mg/kg in S. isoetifolium, summer); Cr was the least concentrated (down to 0.002 mg/kg in H. ovalis, monsoon). S. isoetifolium bioaccumulated heavy metals to higher levels than the other three species. Heavy metals were significantly higher in summer (P < 0.05) and declined through pre-monsoon to monsoon; offshore decayed seagrass deposition carried higher metal concentrations than live seagrass for Mn (16.01 ± 2.01 mg/kg), Pb (0.35 ± 0.02 mg/kg), and Cd (0.54 ± 0.04 mg/kg). The paper is an environmental-bioindicator study; seagrasses are not directly consumed by humans, so it routes as marine-bioindicator context for the heavy-metals literature rather than as a food-contamination measurement.

Key numbers

All concentrations are mg/kg in seagrass tissue; samples dried at 110 °C and ground to fine powder before digestion; basis is dry weight by convention (samples were dried prior to weighing and digestion; the paper does not state the basis explicitly).

Water quality parameters at Thondi coast (Table 1): pH 7.6; water temperature 32 °C; atmospheric temperature 35 °C; salinity 36%; dissolved oxygen 7.4 mg/L.

Manganese (Mn), mg/kg, mean ± SD by species × season (Table 2):

• S. isoetifolium: summer 15.62 ± 1.02; pre-monsoon 13.54 ± 0.92; monsoon 11.91 ± 0.91; post-monsoon 14.76 ± 1.10
• H. pinifolia: summer 8.01 ± 1.23; pre-monsoon 6.22 ± 0.98; monsoon 7.01 ± 0.25; post-monsoon 7.62 ± 0.14
• C. serrulata: summer 6.01 ± 1.2; pre-monsoon 4.98 ± 0.85; monsoon 4.07 ± 0.72; post-monsoon 5.17 ± 0.21
• H. ovalis: summer 7.92 ± 1.25; pre-monsoon 7.24 ± 0.91; monsoon 5.19 ± 0.21; post-monsoon 6.98 ± 0.34
• Concentration order across species: S. isoetifolium > H. pinifolia > H. ovalis > C. serrulata (text §3.2)

Copper (Cu), mg/kg (Table 2):

• S. isoetifolium: 7.41 ± 0.84; 6.92 ± 0.51; 7.04 ± 0.83; 5.81 ± 0.47
• H. pinifolia: 5.92 ± 0.21; 5.11 ± 0.32; 5.42 ± 0.14; 5.81 ± 0.09
• C. serrulata: 3.98 ± 0.14; 3.01 ± 0.12; 3.72 ± 0.19; 3.49 ± 1.01
• H. ovalis: 3.60 ± 0.27; 3.71 ± 0.16; 3.39 ± 0.28; 3.10 ± 0.39
• Concentration order across species: S. isoetifolium > H. pinifolia > C. serrulata > H. ovalis (text §3.2)

Zinc (Zn), mg/kg (Table 2):

• S. isoetifolium: 1.49 ± 0.12; 1.87 ± 0.08; 2.01 ± 0.04; 1.62 ± 0.04
• H. pinifolia: 1.47 ± 0.04; 1.92 ± 0.02; 2.29 ± 0.07; 2.01 ± 0.04
• C. serrulata: 0.92 ± 0.04; 1.11 ± 0.08; 1.36 ± 0.02; 0.87 ± 0.12
• H. ovalis: 0.64 ± 0.02; 1.30 ± 0.03; 1.52 ± 0.04; 1.07 ± 0.01
• Concentration order across species: H. pinifolia > S. isoetifolium > H. ovalis > C. serrulata (text §3.2)

Lead (Pb), mg/kg (Table 2):

• S. isoetifolium: 0.32 ± 0.06; 0.41 ± 0.05; 0.26 ± 0.01; 0.28 ± 0.03
• H. pinifolia: 0.19 ± 0.01; 0.21 ± 0.01; 0.19 ± 0; 0.11 ± 0.01
• C. serrulata: 0.26 ± 0.04; 0.31 ± 0.04; 0.37 ± 0.02; 0.19 ± 0.05
• H. ovalis: 0.12 ± 0.02; 0.18 ± 0.03; 0.07 ± 0.004; 0.12 ± 0.005
• Pre-monsoon peak in S. isoetifolium 0.41 ± 0.05 mg/kg; monsoon low in H. ovalis 0.07 ± 0.004 mg/kg
• Concentration order across species: H. ovalis < H. pinifolia < C. serrulata < S. isoetifolium (text §3.2)

Cadmium (Cd), mg/kg (Table 2):

• S. isoetifolium: summer 0.02 ± 0.002; pre-monsoon BDL; monsoon 0.047 ± 0.003; post-monsoon 0.040 ± 0.009
• H. pinifolia: summer 0.007 ± 0.0; pre-monsoon 0.014 ± 0.001; monsoon BDL; post-monsoon 0.011 ± 0.001
• C. serrulata: summer 0.017 ± 0.01; pre-monsoon 0.02 ± 0.004; monsoon 0.013 ± 0.003; post-monsoon 0.009 ± 0.001
• H. ovalis: summer 0.004 ± 0; pre-monsoon BDL; monsoon BDL; post-monsoon 0.003 ± 0
• Cd was at or below detectable levels in much of the dataset; maximum 0.047 ± 0.003 mg/kg in S. isoetifolium, monsoon
• The paper does not report the BDL numerical threshold

Chromium (Cr), mg/kg (Table 2):

• S. isoetifolium: 0.07 ± 0.004; 0.10 ± 0.007; 0.14 ± 0.009; 0.09 ± 0.004
• H. pinifolia: 0.081 ± 0.008; 0.050 ± 0.006; 0.031 ± 0.006; 0.047 ± 0.002
• C. serrulata: 0.004 ± 0; 0.011 ± 0.002; 0.013 ± 0.008; 0.009 ± 0
• H. ovalis: 0.009 ± 0.001; 0.010 ± 0.002; 0.002 ± 0; 0.013 ± 0.003
• Cr maximum 0.14 ± 0.009 mg/kg in S. isoetifolium, monsoon; Cr minimum 0.002 mg/kg in H. ovalis, monsoon
• The abstract reports “the least metal observed (0.002 mg/kg)” referring to the H. ovalis monsoon Cr value; concentration order across species: H. ovalis < C. serrulata < S. isoetifolium < H. pinifolia (text §3.2)

Offshore decayed seagrass deposition (text §3.3, no separate table): Mn 16.01 ± 2.01 mg/kg (highest of the metals); Pb 0.35 ± 0.02 mg/kg; Cd 0.54 ± 0.04 mg/kg; Cr “least during all seasons” (no numerical value reported). Levels were higher in summer with gradual decrease through pre-monsoon, monsoon, and a slight increase in post-monsoon. The text states heavy metals were higher in offshore decayed seagrass than in the live seagrass species.

One-way ANOVA (text §3.2): Mn and Cu variations across species were significant in summer (P < 0.05); Zn variations across species were highly significant in summer (P < 0.001); Cd variations across species were significant in summer (P < 0.05); Cr variations across species were not significant in any season (P < 0.05 cutoff).

Pearson correlations between metals within species (Table 3, selected significant pairs):

• S. isoetifolium (P < 0.05): strong negative Zn–Mn (r = −0.984); strong negative Cd–Pb (r = −0.982); strong negative Cr–Mn (r = −0.983)
• H. pinifolia (P < 0.01): strong positive Cu–Mn (r = 0.993); strong negative Cr–Zn (r = −0.997)
• C. serrulata (P < 0.05): strong positive Pb–Zn (r = 0.950); strong negative Cr–Mn (r = −0.961)
• H. ovalis (P < 0.05): strong negative Cd–Zn (r = −0.927)

Cluster analysis (Fig. 2, Ward linkage): Two main clusters. Cluster A grouped C. serrulata, H. ovalis, and H. pinifolia (across all four seasons each) into three sub-clusters. Cluster B contained S. isoetifolium alone (across all four seasons). The dendrogram supports the finding that S. isoetifolium bioaccumulates heavy metals distinctly from the other three species.

Methods (brief)

Sample collection: live seagrasses (four species above) collected at low tide from the intertidal zone of Thondi coast, Palk Bay (9°4′N, 79°4′E), Tamil Nadu, southeast coast of India, sampled across summer, pre-monsoon, monsoon, and post-monsoon seasons from April 2019 to March 2020. Dead/decayed offshore seagrass samples were collected from the seashore. Species identification followed Ramamurthy et al. (1992) and Thangaradjou and Bhatt (2018). Water quality parameters (pH, atmospheric temperature, surface water temperature, dissolved oxygen, salinity) were measured at the sampling site during the study.

Sample preparation: washed in seawater on collection to remove debris; transported to laboratory in separate polythene bags. Both live and decayed seagrasses were washed in tap water then distilled water to remove sand and mud. Moisture removed with blotting paper, then samples dried in shade. Dried seagrasses further dried at 110 °C and ground to fine powder.

Digestion: 1 g aliquots weighed and digested overnight with 20 mL concentrated nitric acid. Samples then mixed with 10 mL concentrated nitric acid and perchloric acid in the ratio 4:1. Complete dryness of the acid mixture attained by evaporating at 125 °C on a hot plate. After complete dryness, residue mixed with 20% concentrated nitric acid and made to 50 mL solution. Solution filtered and centrifuged at 4000 rpm. Supernatant used for analysis.

Instrumentation: Shimadzu AA-7000 atomic absorption spectrophotometer (Japan) at wavelengths Cd 228.80 nm, Cr 357.90 nm, Cu 324.75 nm, Pb 217.00 nm, Mn 279.50 nm, Zn 213.85 nm. Heavy metal standards from Merck Genei, Bangalore. Quality assurance and control followed the US EPA protocol for metal analysis. The paper does not report a certified reference material, recovery percentages, method detection limit, or numerical BDL threshold.

Statistical analysis: SPSS Software v20. One-way ANOVA to assess significance of variation among heavy metals and seagrass species. Pearson correlation analysis and cluster analysis (Ward linkage dendrogram) to assess relationships between metals within species and similarities among species.

Limitations: per-cell sample size (replicates per species-season) not stated; no certified reference material or recovery data reported; method detection limit and numerical BDL threshold not reported; speciation not performed (total metal only — Cr-VI vs Cr-III not distinguished; tAs and Hg not assayed); single coastal location (Thondi only); the paper does not report concurrent measurements in surrounding seawater or sediment that would allow bioaccumulation factor calculation.

Verification notes

Fresh ingest 2026-05-18 from raw/Papers Cube Manual Fetch/pasumpon2021.pdf. Notes:

• The matrices vocabulary in docs/gpt-collaboration/system-prompt.md does not include seagrass. Seagrasses are marine angiosperms (taxonomically distinct from seaweeds, which are macroalgae) and are not directly consumed by humans in this study’s geography. The closest existing matrix slugs (seaweed, biota, sediment, fish) would each misrepresent what was measured; seaweed would imply a food matrix that does not apply here. matrices: [seagrass] is used as a new matrix term; this is flagged for taxonomy review. Routing this source to ingredient/product pages would be inappropriate — the paper is environmental-bioindicator context for marine heavy-metal trends and should route to the metals pages (Pb, Cd, Cr, Cu, Mn, Zn) as exposure_only or regulatory_context, not to food pages.
• ingredients: [] and products: [] for the same reason: seagrass is not in the wiki’s ingredient or product taxonomy, and stubbing one would create a routing destination for a non-food matrix that downstream synthesis would have to handle as an exception.
• License set to “Springer Nature exclusive licence (paywalled)” per the PDF cover page: ”© The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature 2021.” This is not CC-licensed; reproduction beyond fair-use quotation requires Springer permission.
• Cr-VI / Cr-III speciation: the paper measures total Cr only (atomic absorption at 357.90 nm captures total Cr without chemical separation). Cr values in this page are tagged as Cr not Cr-VI.
• Brand-firewall: no brand-name food products appear in this paper (the study measures wild seagrasses, not packaged products). Methods naming Shimadzu AA-7000 and Merck Genei standards is permitted under the verification-checklist Exception 2 (scientific-method vendor names).
• Wiki/HMTc firewall: no HMTc threshold comparisons or certification implications drawn; the page reports what the paper measured. Decay-vs-live bioaccumulation difference is recorded as the paper’s finding, not as a synthesis claim.
• Dendrogram in Fig. 2 contains visible typographical errors in the source (“Pre Monsoon” vs “Morsoon”, “Pre Monsoon” vs “Monsoon”, “Pre Monsoon” vs “Monsoon” inconsistencies). The wiki page uses the corrected season names per the paper’s body text, which is internally consistent on summer/pre-monsoon/monsoon/post-monsoon.
• The paper’s body text §3.2 uses a non-standard notation convention for between-species concentration rankings: it writes “increased in the following order: A < B < C < D” (where A is lowest and D is highest, with < carrying its standard mathematical meaning) and also “decreased in the following order: A < B < C < D” (where A is HIGHEST and D is LOWEST, with < used as a loose ranked-listing separator and the verb “decreased” carrying the directional meaning). Both conventions are internally consistent with Table 2 once the verb is the reader’s anchor: e.g., the paper’s Mn “decreased: S. iso < H. pinifolia < H. ovalis < C. serrulata” matches Table 2 where S. isoetifolium has the highest Mn (summer 15.62) and C. serrulata the lowest (monsoon 4.07); the paper’s Zn “decreased: H. pinifolia < S. iso < H. ovalis < C. serrulata” matches Table 2 four-season-mean ranking where H. pinifolia is highest (~1.92) and C. serrulata is lowest (~1.07). The wiki renders all four orderings in the clearer high-to-low > form so that readers do not have to disambiguate the paper’s notation; the rendered orderings match both the paper’s intent and Table 2 data.
• Audit subagent (2026-05-18, verdict REVISE) flagged the Mn (line 42) and Zn (line 58) orderings as silent corrections of paper text that contradicts Table 2. Verified against source: FALSE POSITIVE. The subagent read the paper’s “decreased: A < B < C < D” as A is mathematically less than D (and therefore A is lowest), which would contradict Table 2. The paper’s actual convention (consistent across all four metal orderings in §3.2) is that “decreased” reverses the < direction: A is highest. Under the paper’s convention, the body text is consistent with Table 2, and the wiki orderings reproduce the paper’s intent. No change applied. Pushback documented above.
• Audit subagent also flagged matrices: [seagrass] as ⚠️ for being outside the controlled vocabulary. Verified: this is already disclosed in the Verification notes above (line documenting the new matrix term and routing implications). No additional change applied; the existing Verification note is the intended interim documentation pending Karen’s taxonomy-review pass.
• Audit subagent verdict pushback: REVISE issued primarily on the ordering finding, which is a false positive (paper-notation convention misread). The matrices flag is an acceptance of the existing Verification note. No content changes to the wiki page on either finding. Final disposition: audited-revised with one false-positive rejection documented and one matrices-vocabulary item left as already-disclosed.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Description
ce3e07c	2026-05-28	activation | Vercel DATACITE env slots set, curators.md filled with founder entry + six scoped reviewer invitations, peer-review onboarding playbook drafted
51400b9	2026-05-28	audit-queue: gasparik2017-wild-boar-slovakia-metals audited-revised