**Heavy Metals Concentrations (mg/L) at Depths DWS IWS ALS SWS Shallow Middle Bottom 4. Conclusions**

**4. Conclusions**

Cd 0.0014 0.0023 0.0015 0.005 0.01 0.01 0.01 Cr 0.0002 0.0002 0.00018 0.1 0.1 0.05 0.16 Cu 0.0012 0.0029 0.0032 1.3 0.2 0.05 - Fe 0.0011 0.0018 0.0035 0.3 - - - Mn 0.0014 0.0021 0.0006 0.05 2 1 1 Ni 0.0047 0.0018 0.0018 - 0.2 - 0.144 This study was conducted to analyze the baseline values of the total suspended solid and heavy metals during and post-COVID-19 pandemic. The study reports that concentrations of heavy metals are under permissible limits of National Water Quality Standards of Malaysia, Food and Drug Administration, and standards of drinking water, irrigation water, and aquatic life. However, there are variations in different depths at the same sampling site. The possible reason for those heavy metal values that suddenly drop from one site to another could be the high settling tendency in Kerian River due to binding

Pb 0.0009 0.0008 0.0012 0 5 0.05 0.005

capacities with other existing components of water matrix such as micro particles or micro vegetation. They may be in suspended, colloidal, or dissolved form. Whereas, for those heavy metal values that suddenly raised from one site to another, the possible reason could be an anthropogenic source. High concentrations of Ni, Zn, and Fe were reported at shallow, middle, and bottom depths, respectively. Overall, the possible reason for the lack of heavy metal pollution may be due to COVID-19 restrictions on anthropogenic activities. Whereas, before the post-pandemic period, heavy metal values increased from 60% to 100% from during pandemic conditions. This confirms that the increment is due to anthropogenic activities after releasing COVID-19 restrictions. Furthermore, no significant effect was observed on total suspended solid values in post-pandemic conditions.

**Author Contributions:** Conceptualization, M.N.A. and E.A.B.; Data curation, E.A. and J.B.J.; Formal analysis, M.N.A., M.T.A., J.B.J. and M.D.; Investigation, E.A. and M.D.; Methodology, M.N.A., M.T.A. and J.B.J.; Project administration, E.A.B.; Resources, M.D.; Supervision, E.A.B.; Writing—original draft, M.N.A.; Writing—review and editing, M.T.A. and E.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was funded by Research Creativity and Management Office, Universiti Sains Malaysia. The authors would like to acknowledge the grant RU Top-Down 1001/PAERO/870052.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

### **Appendix A**

**Table A1.** Laboratory results of eight heavy metals (ppm) with their standard deviations at different depths.



**Table A1.** *Cont.*

### **References**

