Valencia et al. 2021 — Pb and Cd in cultured Crassostrea iredalei oysters, Cañacao Bay, Philippines

Valencia and colleagues measured lead and cadmium in 214 cultured slipper-cupped oysters (Crassostrea iredalei) and parallel surface-seawater samples taken from three sampling stations across the Cañacao Bay mariculture area (Cavite Province, Luzon, Philippines) over the four months October 2016 to January 2017, spanning the wet-to-dry seasonal transition. The bay is a section of the larger Manila Bay and is bordered by a residential coastal community, the Cavite-Manila ferry route, and a steel corporation outfall. Concentrations were quantified by inductively coupled plasma optical emission spectrometry (ICP-OES) on a Shimadzu ICPE-9810 after dry-ashing acid digestion, with results expressed in mg/kg for oyster soft tissue and mg/L for seawater. Tissue Pb and Cd ranged below the maximum permitted levels set by FAO, FSAI, and FSANZ in every month at every station; target hazard quotients (THQ) and total target hazard quotient (TTHQ) computed for a Filipino adult reference (65 kg BW, 71-year exposure duration, 3.50 g/person/day oyster ingestion) were below 1.0 in every monthly cell, indicating no appreciable non-carcinogenic risk for the modelled adult population. Pb in oyster tissue varied significantly between wet and dry seasons (p<0.05); Cd did not. No significant differences in either metal were observed across the three sampling stations.

Key numbers

Units: mg/kg fresh weight for oyster soft tissue (whole soft-tissue homogenate of shucked, pooled specimens, dry-ashed and dissolved in 50% HCl before ICP-OES analysis); mg/L for seawater (filtered, acidified to 10% HNO₃). Detection limit for Pb in oyster tissue was 0.1 mg/kg; values below detection are reported as “<0.1” and were computed at 0.1 mg/kg for THQ purposes. Detection limit for Pb in seawater was 0.05 mg/L; for Cd in seawater 0.01 mg/L; the entire seawater dataset fell below these limits.*

Pb and Cd in oyster soft tissue by sampling station and month — Table 1

Cells are mg/kg fresh weight. Asterisk (*) denotes below the 0.1 mg/kg analytical detection limit.

• October (wet season): all three stations below the 0.1 mg/kg Pb detection limit; Cd mean 0.083 ± 0.006 mg/kg, the highest monthly Cd mean of the series.
• November (wet season): Pb mean 0.133 ± 0.056 mg/kg; Cd mean 0.027 ± 0.006 mg/kg.
• December (dry season): Pb mean 0.4 ± 0.1 mg/kg, the highest monthly Pb mean; Cd mean 0.043 ± 0.006 mg/kg.
• January (dry season): all three stations below the 0.1 mg/kg Pb detection limit; Cd mean 0.027 ± 0.006 mg/kg.
• Aggregate range as stated in the abstract: Pb < 0.1 to 0.4 ± 0.1 mg/kg; Cd 0.027 ± 0.006 to 0.083 ± 0.006 mg/kg.

Comparison against regulatory maximum levels (Table 1 right-hand columns)

Maximum standard limits (mg/kg) summarised by the authors against which the Cañacao Bay values were compared:

• FAO permissible limit for bivalve food: 1 mg/kg for both Pb and Cd (FAO 2003).
• FSAI (Ireland): 1.5 mg/kg Pb; 1.0 mg/kg Cd (FSAI 2009).
• FSANZ (Australia / New Zealand): 2.0 mg/kg for both Pb and Cd (FSANZ 2013).
• Every monthly mean Pb and Cd in C. iredalei fell below all three regulatory ceilings.

Pb and Cd in seawater

• Pb concentration in surface seawater across the entire study period: < 0.05 mg/L (below analytical detection limit; below DENR Philippines Class SA limit and ASEAN Marine Water Quality Criteria).
• Cd concentration in surface seawater across the entire study period: < 0.01 mg/L (below analytical detection limit; below DENR Class SA limit and ASEAN criteria).
• Cd concentrations in the water column ranged from 0.2 to 0.9 mg/kg (sic — likely the authors’ textual gloss of a comparison study, not new Cañacao seawater values; the seawater dataset itself was below detection throughout).
• Comparison point: Cañacao Bay Pb and Cd in water were lower than values reported by Sia Su et al. (2009) for Manila Bay clams (Mercenaria sp.), which had 7.38 mg/kg Pb and 1.72 mg/kg Cd in clam tissue (oysters here were 15× lower than Sia Su Pb and 19× lower than Sia Su Cd, per the discussion text).

Target hazard quotients — Table 2

Computed per US EPA Region III risk-based equation: THQ = (EF × ED × FIR × C) / (RFD × WAB × TA) × 10⁻³ where EF = 365 days/year, ED = 71 years, FIR = 3.50 g/person/day, RFD Pb = 0.004 mg/kg-day, RFD Cd = 0.001 mg/kg-day, WAB = 65 kg, TA = 365 × 71. Pb THQ values for months below detection were computed at C = 0.1 mg/kg (the detection limit).

• Highest monthly THQ Pb: 5.385 × 10⁻³ (December).
• Highest monthly THQ Cd: 4.487 × 10⁻³ (October).
• Highest monthly TTHQ: 7.718 × 10⁻³ (December).
• All monthly THQ and TTHQ values are at least two orders of magnitude below the 1.0 threshold above which a non-carcinogenic health risk would be indicated.

Seasonal and station comparisons

• Pb in C. iredalei differed significantly between wet (October-November) and dry (December-January) seasons (p<0.05). The authors attribute the higher dry-season Pb to lower precipitation and salinity-driven dilution effects.
• Cd in C. iredalei did not differ significantly between wet and dry seasons (p>0.05).
• No statistically significant differences in Pb or Cd were observed among the three sampling stations (p>0.05).

Shell-length / metal correlations (Figures 2 and 3)

• Mean C. iredalei shell length ranged from 48.79 ± 4.42 mm to 50.79 ± 3.86 mm across the sampling period.
• Pb-vs-shell-length linear regression: R² = 0.1067, r = 0.327 — very weak positive correlation, not statistically significant (p>0.05).
• Cd-vs-shell-length linear regression: R² = 0.034, r = 0.002 — no correlation.

Physicochemical parameters of station seawater — Table 3

• pH, dissolved oxygen, and turbidity did not differ significantly between wet and dry seasons (p>0.05).
• Seawater temperature differed significantly between seasons; wet season was warmer (Southwest Monsoon) than dry season (Northeast Monsoon).

Methods (brief)

Three sampling stations were established within the Cañacao Bay mariculture area, geolocated by Garmin GPSMAP 62s. Oyster samples (52-57 per month, 15-20 per station per month, 45-55 mm marketable shell length) and surface seawater (≤2 m depth) were collected monthly from October 2016 through January 2017 (n = 214 oysters total). Oyster samples were transported below 4°C in polyethylene tagged bags; seawater was collected in 10%-HNO₃-pre-washed black polyethylene bottles and rinsed with deionised water. Oysters were thawed, washed with deionised water to remove mantle/gill particles, shucked, pooled, and homogenised in a stainless-steel blender. Dry-ashing digestion: 10 g fresh sample placed in an evaporating dish, dried in a vacuum oven, 1 mL concentrated HNO₃ added and evaporated, then ashed at 450°C for 5 h in a muffled furnace (a second 1 mL HNO₃ + 2 h ashing applied if ashing incomplete). The ash was dissolved in 50% HCl, brought to 25 mL, and diluted at least 1:5 before ICP-OES analysis. Heavy-metal analysis was performed by Shimadzu ICPE-9810 ICP-OES at working wavelengths 220.353 nm (Pb) and 226.502 nm (Cd) per US EPA 1996 calibration standards (Morrison et al. 2020 cited for wavelength choice). Detection limit for Pb in oyster tissue was 0.1 mg/kg; detection limit for Pb in seawater was 0.05 mg/L and for Cd in seawater was 0.01 mg/L. Physicochemical parameters were measured in situ in triplicate using an ExStik II DO600 (FLIR Systems) for temperature and dissolved oxygen and an ExStik II pH meter; turbidity was measured later in the laboratory on an APEL PD-303UV spectrophotometer at 540 nm. THQ and TTHQ were computed from the US EPA Region III risk-based concentration equation with Filipino-adult reference parameters; statistical comparisons used unpaired and paired t-tests, ANOVA across stations, and Pearson correlation / linear regression for shell-length-vs-metal, all executed in SPSS Statistics 20.0 (IBM) and GraphPad Prism 7 (GraphPad Software).

Limitations

• Single-bay study with a four-month sampling window spanning only the wet-to-dry transition; values do not generalise to other Philippine mariculture areas, to other Crassostrea species, or to other seasons of the year. The authors recommend continuous monitoring for future temporal coverage.
• ICP-OES detection limits are coarser than ICP-MS for trace Pb (0.1 mg/kg for tissue; 0.05 mg/L for water); a substantial fraction of the tissue Pb dataset (October and January means at every station) and the entire seawater Pb and Cd dataset fell below detection. THQ Pb values for below-detection months were imputed at the detection limit (0.1 mg/kg), which is conservative for the risk-quotient computation but obscures the true central tendency of below-detection cells.
• THQ assumes lifetime average Filipino-adult ingestion at 3.50 g oyster per person per day (FNRI-DOST 2013) and may underestimate risk for higher-consumption coastal communities, susceptible populations (children, pregnant women), or seasonal binge-consumption patterns. The authors themselves note that THQ for children would likely be higher and that risk varies with age group, locality, and consumption frequency.
• Speciation was not measured: only total Pb and total Cd (atomic-emission lines for elemental Pb and Cd). Methylated lead species and Cd-protein complex distribution within oyster tissue were not characterised.
• Oysters were homogenised whole-soft-tissue without separating organs (digestive gland, gonad, gill, mantle), which masks tissue-specific accumulation patterns that may matter for partial-consumption scenarios (e.g., consumers who remove the dark glandular tissue).
• THQ Pb arithmetic depends sensitively on which value is used for below-detection cells; an October Pb THQ of 1.346 × 10⁻³ “computed at 0.1 mg/kg” is implicitly an upper-bound, not a central estimate, of the true October Pb risk for this matrix.
• The seasonal Pb difference (higher in December dry season) is attributed by the authors to lower wet-season dilution; this is plausible but the four-month series cannot distinguish seasonal dilution effects from short-lived point-source events (e.g., a specific December discharge from the adjacent steel corporation).
• The paper offers no quantification of the steel-corporation outfall load, and the observed lack of station-to-station differences argues against a strong, persistent Station-3 point-source signal across the four months sampled.

Implications

• Occurrence and routing for shellfish ingredient page: the source adds a low-tier Pb and Cd dataset for cultured tropical oyster (C. iredalei) from a Manila Bay sub-system. Tissue Pb and Cd means are well below the FAO 1 mg/kg permissible limit and below the Sia Su et al. (2009) Manila Bay clam values cited in the discussion. The source is routeable to shellfish, bivalve-molluscs, molluscs, seafood, shellfish, and seafood as occurrence evidence for a Philippine mariculture matrix.
• Certification context: not threshold-bearing for HMTc work. The paper applies external regulatory ceilings (FAO 1 mg/kg, FSAI 1.0-1.5 mg/kg, FSANZ 2 mg/kg) without proposing new thresholds and uses US EPA RfD-based THQ to characterise health risk against an exposure-quotient threshold of 1.0. Any HMTc standards-setting for shellfish should treat the Cañacao Bay dataset as one Asia-Pacific contributor among many in a percentile-pool admission rather than as a basis for an HMTc-specific limit.
• Courses: usable as a worked example in the seafood-and-aquaculture module of how THQ and TTHQ are computed for a defined population (Filipino adult, 65 kg, 71-year ED, 3.50 g/day), how ICP-OES detection limits propagate into upper-bound risk estimates for below-detection cells, and how seasonal dilution effects can produce statistically significant Pb-but-not-Cd differences in tropical mariculture.
• App (if/when shipped): Filipino-adult oyster Pb and Cd central tendencies (≤0.4 mg/kg Pb, ≤0.083 mg/kg Cd) are of the order of magnitude that would render a typical 3.50 g/day serving low-risk in a contamination-likelihood estimator; higher-consumption scenarios should still be flagged.
• Microbiome: out of scope. The source does not characterise oyster gut microbiota or metal-microbe interactions.
• Cross-source signal: complements romero-estevez2020-bivalves-santa-rosa-ecuador (Ecuadorean mangrove Anadara, Pb/Cd/Cr), chou-uthe1993-cadmium-american-lobster-belledune (Canadian Atlantic lobster, Cd point-source), gongora-gomez2017-oysters-gulf-california-metals (Mexican C. gigas, eight-metal panel), and the related Philippine bivalve dataset in raju2021-bivalves-cagayan-philippines as a comparative Philippine mariculture point. Treated together, these are an evidence base for the bivalve-mollusc and shellfish ingredient-page occurrence summaries.

Wiki pages this source may touch

• lead — Philippine mariculture occurrence; seasonal dilution effect; ICP-OES detection-limit treatment in THQ computation.
• cadmium — Philippine mariculture occurrence; no significant seasonal effect in tissue Cd.
• shellfish — Pb and Cd occurrence in cultured Crassostrea iredalei, Manila Bay, four-month series.
• bivalve-molluscs — same.
• molluscs — same.
• seafood — same.
• shellfish — Pb and Cd in cultured oyster product matrix; sub-FAO/FSAI/FSANZ limits.
• seafood — broader seafood-occurrence context.
• raju2021-bivalves-cagayan-philippines — companion Philippine bivalve dataset for cross-source pooling on PH occurrence.
• romero-estevez2020-bivalves-santa-rosa-ecuador — companion mangrove-bivalve dataset (Ecuador) for international comparison.
• gongora-gomez2017-oysters-gulf-california-metals — companion cultivated-oyster (C. gigas) dataset (Mexico).

Verification notes

• 2026-06-03 — Fresh source-page ingest from raw/manual-fetch/Kimi_Agent_Download Corruption Issue/seafood_papers/04_Shellfish/. No prior wiki page (DOI 10.22515/sustinerejes.v5i2.159 not previously ingested; cite-key valencia2021-canacao-bay-oyster-pb-cd not previously used; raw_handle KADC_heavy-metal-accumulation-and-risk-assessment-of-le not previously ingested).
• Full paper pages 1-10 (abstract, methods, all results/tables 1-3, figures 2-3, discussion, conclusion, opening of references) read directly from the PDF. Tables 1-3 numeric values transcribed verbatim, including the (*) “below detection limit” footnotes and the “*computed at 0.1 mg/kg” annotation on the October and January Pb THQ rows.
• Speciation flags: the source measures total Pb (elemental Pb by ICP-OES at 220.353 nm) and total Cd (elemental Cd by ICP-OES at 226.502 nm). No methylmercury, no inorganic-arsenic-vs-total-arsenic distinction (arsenic is not measured in this study).
• Units preserved as the source reports them: mg/kg for oyster soft tissue (fresh-weight basis; the dry-ashing digestion is sample preparation, not a basis change), mg/L for seawater, dimensionless THQ/TTHQ. No silent conversion to ppb or ppm.
• Method-vendor names retained per CLAUDE.md Part 12 Exception 2: Shimadzu ICPE-9810 (ICP-OES instrument), Garmin GPSMAP 62s (geolocation), FLIR Systems ExStik II DO600 and pH meter (in-situ physicochemical), APEL PD-303UV (turbidity spectrophotometer), IBM SPSS Statistics 20.0 (statistical software), GraphPad Prism 7 (statistical software).
• Brand-firewall: no consumer-brand contamination attributions appear in the source. The steel corporation adjacent to Station 3 is not named in the paper and is not named here.
• Part 2 wiki/HMTc firewall: this page reports the Cañacao Bay Pb and Cd values, the THQ/TTHQ computation, and the FAO/FSAI/FSANZ ceilings the authors cite. It does not propose, soften, or strengthen any HMTc shellfish threshold; the Implications section is restricted to noting routing destinations and the source’s status as one contributor among many for any future HMTc percentile-pool analysis.
• One textual oddity in the source (resolved against Table 1, no correction to wiki values needed): page 4 of the PDF (paragraph immediately above the oyster-Pb paragraph that precedes Table 1) reads “Cd concentrations ranged from 0.2 mg/kg to 0.9 mg/kg levels.” This sentence is inconsistent with Table 1 (Cd-in-oyster individual-station values 0.02-0.09 mg/kg; monthly means 0.027-0.083 ± 0.006 mg/kg) and with the abstract (Cd 0.027 ± 0.006 to 0.083 ± 0.006 mg/kg), and the 0.2-0.9 mg/kg range is exactly 10× the actual Table 1 Cd-in-oyster individual-station range. The most parsimonious reading is a decimal-place typographical error in the source itself (intended Cd-in-oyster-tissue range, miswritten by one order of magnitude); the surrounding paragraph context (Gobas 2001 cited for detection-limit discussion, sediment-binding gloss) makes the “comparison study” reading less likely. The Key-numbers table values for Cd in Cañacao oysters come from Table 1 and the abstract and are internally consistent at the 0.02-0.09 mg/kg order of magnitude.
• 2026-06-03 — Fresh-context audit subagent (verdict REVISE) flagged two ⚠️ concerns: (a) the 0.2-0.9 mg/kg textual oddity is most plausibly a decimal-place typo (10× the actual Table 1 Cd-in-oyster range), not a comparison-study gloss as the initial draft hedged; (b) the “15-20 samples per station per month” wording read as if quoted from source but is a derived figure consistent with the monthly total of 52-57 divided across three stations. Both ⚠️ concerns verified independently against the PDF and applied: typo-reading clarified in this Verification-notes section above and sample_population reworded to reflect that the per-station figure is consistent-with rather than verbatim-quoted. No ❌ definite-error findings.

Page history

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