Overview
Ashfaq and colleagues measured zinc, chromium, iron, and lead in edible fruit tissue of three citrus species (Citrus limetta, C. reticulata, C. sinensis) grown under canal water irrigation (CW-I) and domestic wastewater irrigation (DWW-II) at two sites in the Sargodha district, Punjab, Pakistan. Fruits were harvested at the edible ripeness stage, washed, oven-dried at 70 degrees C, ground, and acid-digested before analysis by atomic absorption spectrophotometry (AAS). The study also measured the same metals in irrigation water and orchard soil. Cadmium was not analyzed. The primary finding relevant to food safety is that all four metals in citrus fruit tissue remained below permissible limits regardless of irrigation source, and all target hazard quotients were below 1.
Key numbers
Fruit tissue concentrations (mg/kg dry weight, mean +/- SEM, n = 3 per site per species):
| Species | Site | Zn (mg/kg) | Cr (mg/kg) | Fe (mg/kg) | Pb (mg/kg) |
|---|---|---|---|---|---|
| C. limetta | CW-I | 1.08 +/- 0.04 | 0.04 +/- 0.01 | 1.96 +/- 0.06 | 0.031 +/- 0.003 |
| C. limetta | DWW-II | 1.58 +/- 0.07 | 0.10 +/- 0.01 | 3.44 +/- 0.10 | 0.011 +/- 0.001 |
| C. reticulata | CW-I | 1.33 +/- 0.06 | 0.06 +/- 0.01 | 2.13 +/- 0.07 | 0.025 +/- 0.002 |
| C. reticulata | DWW-II | 1.33 +/- 0.05 | 0.08 +/- 0.01 | 3.20 +/- 0.09 | 0.010 +/- 0.001 |
| C. sinensis | CW-I | 1.17 +/- 0.04 | 0.06 +/- 0.01 | 2.32 +/- 0.08 | 0.015 +/- 0.002 |
| C. sinensis | DWW-II | 1.50 +/- 0.06 | 0.08 +/- 0.01 | 3.13 +/- 0.09 | 0.010 +/- 0.001 |
| Permissible limit (fruit) | n/a | 60 | 2.3 | 20 | 0.1 |
All fruit metal concentrations fell below the stated permissible limits (Table 2 regulatory thresholds and Table 4 food safety guidelines). THQ values for all metals and all varieties remained below 1 under both irrigation regimes (Fig. 9). EDI values for all metals remained below internationally recommended tolerable daily intake limits (Fig. 8).
LOD values: Zn 0.015, chromium (Cr) 0.050, Fe 0.050, lead (Pb) 0.050 mg/L. LOQ values: Zn 0.050, Cr 0.100, Fe 0.160, Pb 0.033 mg/L. Calibration R-squared at least 0.999 for all metals. Recovery from certified reference material (NIST SRM 1643f for water; BCR-141R for soil) was 80 to 120 percent with less than 5 percent uncertainty. Intra-day precision (RSD) was below 5 percent.
Methods
Field-based comparative study at two citrus-growing sites in Sargodha district. CW-I site (Chakiyan Phularwan, Tehsil Bhalwal) used canal water exclusively. DWW-II site (Chak No. 79 N.B., Tehsil Sargodha) used domestic wastewater. Within each site, three geographically distinct locations were sampled, with three orchards per location, one tree per orchard, yielding n = 3 biological replicates per site per species. Fruits harvested at edible ripeness, washed, oven-dried at 70 degrees C for 48 hours, ground, and acid-digested with HNO3 before AAS analysis (PerkinElmer). Results reported on dry weight basis. Two-way factorial ANOVA with Tukey HSD post hoc test.
Cadmium was not included in the analyte panel. The study reports dry-weight fruit concentrations; fresh-weight values require moisture-content adjustment that the paper does not provide. The two irrigation sites differ in soil type (sandy alluvial at CW-I vs alluvial loam at DWW-II), so observed differences reflect combined irrigation and site effects, not irrigation source alone.
Evidence fitness
B-tier. The study provides replicated field data (n = 3 per cell) from a real agricultural setting with QC (CRM verification, recovery, RSD). Limitations: only two sites (one per irrigation type), so site and irrigation effects are confounded; cadmium was not measured; dry-weight basis without moisture data prevents direct comparison to wet-weight food standards; and the three citrus species may not represent the full diversity of commercially relevant citrus cultivars.
Related evidence
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