Water contamination is a critical issue in plant growth since the contaminated water can cause abnormality to the plants when phototoxicity occurs. Phytotoxicity can happen when plants use contaminated water for photosynthesis because anything chemical would cause an adverse reaction. For organic contaminants, samples from ammonium nitrate and pesticides are tested and the absorbance peak for contaminants are 363nm and 361nm respectively. Besides that, the heavy metal sample is prepared by mixing up white powder of zinc oxide with water to produce a concentrated heavy metal solution with an absorbance peak at 405nm. Lake water from Universiti Sains Islam Malaysia (USIM) that are used for irrigation systems also are collected to check any organic or heavy metal contaminants. The Ocean Optic spectrometer shows an absorbance peak at 361nm, while the low-cost spectrometer lies between 300nm to 400nm. The absorbance spectrum in this region shows the highest peak excitation of organic particles. It proves that pesticides are organic contaminants and the presence of this compound in water used for irrigation systems can cause abnormality in the plants growth. Therefore, appropriate, and systematic water supplies are indispensable in agricultural production systems to produce healthy growing plants for consumers.

Water pollution is a critical issue since it can severely affect health and the environment. The purpose of the study is to develop a portable spectrometer (ESP32-based spectrometer) to detect chemical contaminants in irrigation water by observing the light absorbance of contaminants. ESP32 and a light sensor (photodiode) were respectively, used as the main controller and detector of the portable spectrometer. It was developed based on optical dispersion and Beer–Lambert law theory. The light absorbance of different types of contaminants was displayed in a Blynk application for real-time monitoring. The samples were also tested using a lab-based spectroscopy method, ultraviolet-visible (UV-Vis) spectrometer. The spectral range of the measurement is from 350 nm to 700 nm and the standard error of the ESP32-based spectrometer is from 0.01 to 0.05. Five water samples were tested, consisting of ammonium nitrate, organic pesticide, zinc oxide and two different reservoirs used for irrigation. The absorption peaks of the ammonium nitrate and organic pesticide are 363 nm and 361 nm, respectively. Zinc oxide shows the absorbance peak at 405 nm, whereas both reservoirs show absorbance peaks lie in the region from 300 nm to 370 nm. Therefore, this study shows that different types of contaminants can absorb light only at specific wavelength regions by considering the concentration of samples. The developed ESP32-based spectrometer can be applied for on-site water quality monitoring as it is portable, light, simple and can be monitored in real time using multiple devices.