In Vitro Assessment Of Cadmium Bioavailabilitv And Toxicity In Contaminated Soils And Food Crops For Human Health And Environmental Risk Assessment

The cadmium (Cd) contamination of agricultural soils and food crops grown in these soils can pose long term environmental and health implications. Therefore an understanding of Cd bioaccessibility, bioavailability and toxicity in human through ingestion of soil and food crops is needed. The current study was aimed to establish Caco-2 cell/HL-7702 cell model to assess the Cd bioavailability/toxicity from two different soils and food crops grown on these soils. Using this in vitro digestion coupled with Caco-2/HL-7702 cell models. We identify the minimum concentration of Cd directly from two different textured soils (Yellow soil, Calcareous soil) and food crops (rice, Chinese cabbage) grown on these soils that can initiate toxicity in human liver (HL-7702) cells. The main results are summarized as below.1. In this study, human intestinal cell line (Caco-2 cells) and normal human liver cell line (HL-7702 cells) were used to investigate the toxicity and bioavailability of Cd to both cell lines, and to validate these cell lines as in vitro models for studying Cd accumulation and toxicity in human intestine and liver. Results showed that Cd uptake by both cell lines increased in a dose-dependent manner and its uptake by Caco-2 cells (720.15 μmg-1 cell protein) was significantly higher than HL-7702 cells (229.01 μgmg-1 cell proteins) at 10 mgL-1. A time-　and dose-dependent effect of Cd on cytotoxicity assays (LDH release, MTT assay) was observed in both Cd-treated cell lines. The activities of antioxidant enzymes and differentiation marker (SOD, GPX and AKP) of the HL-7702 cells were higher than those of Caco-2 cells, although both of them decreased significantly with raising Cd levels. The results from the present study indicate that Cd above a certain level inhibits cellular antioxidant activities and HL-7702 cells are more sensitive to Cd exposure than Caco-2 cells. However, Cd concentrations< 0.5 mg L-1 pose no toxic effects on both cell lines.2. Ingestion of contaminated soil has been identified as an important exposure pathway of cadmium (Cd) for humans, especially for children by so called hand-to-mouth activities. In this study Cd bioaccessibility, bioavailability and toxicity to human from ingestion of Cd contaminated soils was assessed by using in vitro digestion coupled with Caco-2/HL-7702 cell model. Results indicated that Cd bioaccessibility in gastric phase (44.3 to 89.8%) and in small intestinal phase (35.69 to 46.15%) were found to be significantly higher in yellow soil (YS) than calcareous soil (CS) with the corresponding values of 28.65%　to 56.81%　and 6.08%　to 27.30%　%　respectively. Cadmium bioavailability was higher (13.50-35.40%), when YS Cd concentrations were used, whereas lower values (3.5-10.76%) were derived when CS Cd concentrations were employed in calculations. Toxicity assays revealed that Cd concentrations (>0.78μg) transported from YS and CS to normal human liver (HL-7702) cells is able to induce oxidative (MDA, H2O2) stress by weakens the antioxidant (SOD, GPx) enzyme activities in HL-7702 cells. The results of this study suggested that acidic (YS) soils of Cd contaminated areas can contribute to a higher dietary intake of Cd than that of high pH (CS) soils.3. Cadmium (Cd) enters the food chain from polluted soils via contaminated cereals and vegetables therefore an understanding of Cd bioaccessibility, bioavailability and toxicity in human through rice grain is needed. This study assessed the Cd bioaccessibility, bioavailability and toxicity to human from rice grown on Cd contaminated soils using in vitro digestion method combined with Caco-2/HL-7702 cell model. Cadmium bioaccessibility (18.45-30.41%) and bioavailability (4.04-8.62%) were found to be significantly higher in yellow soil (YS) rice than calcareous soil (CS) rice with the corresponding values of 6.89-11.43%　and 1.77-2.25%, respectively. Toxicity assays showed an initial toxicity in YS rice at 6 mg kg-1 Cd while CS rice didn’t show any significant change due to low Cd concentrations. The acidic soils of Cd contaminated areas can contribute to a higher dietary intake of Cd. Therefore, it is imperative to monitor Cd concentration in rice to minimize human health risk.4. The minimum concentration of cadmium (Cd), by Chinese cabbage grown on Cd contaminated soils that can initiate toxicity in human liver cells using in vitro digestion coupled with Caco-2/HL-7702 cell models was studied. Cadmium bioaccessibility in the gastric phase for yellow soil (YS) cabbage (40.84%) and calcareous soil (CS) cabbage (21.54%) was significantly higher than small intestinal phase with the corresponding values of 21.2% and 11.11% respectively. Cadmium bioavailability was higher in YS cabbage (5.27%-14.66%) than the CS cabbage (1.12%-9.64%). Cadmium concentrations (>0.74μg) transported from YS and CS cabbage was able to induce oxidative (MDA, H2O2) stress by inhibiting antioxidant (SOD, GPx) enzyme activities in human liver cells (HL-7702). Additionally the study revealed that the ingestion of Cd contaminated Chinese cabbage grown in acidic soil (Yellow soil) weakened the antioxidant defence system under all levels of contamination (2,6,9 mg.kg-1) which ultimately escalated the oxidative stress in liver cells, however, in case of CS cabbage, a marked oxidative stress was observed only at 9 mg kg-1 Cd level of soil. Therefore, it is necessary to monitor Cd concentrations in leafy vegetables grown on acidic soils to minimize human health risk.