Uptake of Heavy Metals by Rice Plants in Ranau Valley Paddy Field (Sabah)

Transcription

1 Uptake of Heavy Metals by Rice Plants in Ranau Valley Paddy Field (Sabah) Roslaili Abdul Aziz, Sahibin Abd Rahim, Ismail Sahid, Wan Mohd Razi Idris and Md. Atiqur Rahman Bhuiyan

2 High rainfall during the rainy season caused Ranau ultrabasic soil to be eroded which then enters into the Ranau Valley paddy fields through irrigation systems and overflowing flooding streams. Clear indicator of ultrabasic soil contamination: (i) Oily water, (ii) Reddish paddy soil. The aim of this study is to determine the bioavailability of heavy metals in paddy fields contaminated by ultrabasic soil. Introduction

3 This paddy field is contaminated with ultrabasic soils which contained high concentrations of heavy metals such as Co, Ni and Cr. 15 top soil samples at 0-30 cm depth and 15 rice plants were sampled. Total heavy metals in soil were extracted with concentrated HNO3HClO4 (v/v 3:1) [5]. Heavy metals in rice grain samples were extracted according to the method described in AOAC [6]. Concentrations of As, Cd, Co, Cr, Cu, Ni and Zn in soil and plant extracts were determined using ICPMS after dilution. Biological absorption coefficient (BAC) was calculated based on the ratio of heavy metals content in rice grain and in soils [7, 8]. Materials and Methods

4 Total heavy metals in paddy soils [mg/kg]: Paddy Soils As Cd Co Cr Cu Ni Zn Min 1.38 bdl Max Mean SD *MAC *TAV *MAC = maximum allowable concentration, *TAV = trigger action value [18] bdl = below detection limit Heavy metals concentration above the TAV requires remediation on the soils [9]. Results and Discussion

5 Correlation analysis shows that there is a significant positive correlation at 0.1 percent level between As with Cu and Zn (r=0.988***, r=0.984*** respectively), Co with Cr and Ni (r=0.960***, r=0.972*** respectively), Cu with Zn (r=0.999***) and Cr and Ni (r=0.995***). Positive correlations indicate that the metals enriched together either through: (i) precipitation, (ii) Fe-Mn oxide formation, or (iii) adsorption by organic matter and clay mineral in soil. Very high correlation between Co, Cr, and Ni which is naturally high in ultrabasic rocks could also indicate that these metals are present in the ultrabasic soil contaminant in the paddy field. Results and Discussion

6 Heavy metals concentration in Ranau rice grain samples (mg/kg): Rice Samples Min Max Mean SD As bdl Normal conc. [18] Critical conc. [18] 1-20 Cd Co Cr Cu Ni Zn All heavy metal concentrations are within the normal concentration range and well below the critical concentration in plants based on Kabata-Pendias [9]. Results and Discussion

7 BAC classifications for Ranau rice plants: (i) moderate accumulator of Cd (0.87) and Zn (0.38), (ii) low accumulator of As (0.01), Co (0.02) and Cu (0.03), and (iii) non-accumulator of Cr (0.00) and Ni (0.00). High concentration of heavy metals in soil do not necessarily enrich the metals in rice grain, suggesting that there is a mechanism existing in the plant to filter harmful concentrations of heavy metals from entering the plant or the rice grain. Results and Discussion

8 The present results showed that high concentration of heavy metals in soil do not necessarily increase the concentration in the rice grain. The low concentration of heavy metals in the rice grain is elucidated by low bioavailability of heavy metals as indicated by low BAC values. Conclusion

9 Thank You UKM & UniMAP