1.1 Background of study

Heavy metals are common pollutants from anthropogenic sources discharges into the environment especially water body such as river which negatively affect both water quality and aquatic ecosystems. River is an important element to the human and other living organisms as it provide fresh water for daily human activities such as domestics, agriculture, industrial use and also source of food. Uncontrolled and excessive exploitation of river resource will bring destruction to the environment and pollution to the water sources which are hard to restore (Gasim et al. 2015). Growing human population, industrial expansion, agricultural, development on river banks and other anthropogenic activities are common factor that causing pollution to the river. Anthropogenic activities did not just produce massive waste into the aquatic environment, it may also altered the equilibrium in aquatic ecology.

In general, heavy metal are element with atomic number 22 until 92 in period table and classified into essential and non-essential heavy metal. Essential heavy metal such as Zn and Mg are required by human body in trace element for biological function, but can produce adverse health effect if present in high concentration. Non-essential heavy metal such as Hg and Pb are readily toxic even in low concentration, and can bring adverse effect including death if exposed to human. Presence of heavy metal in the environment can be caused by either natural or anthropogenic (Shuhaimi et al. 2010). Hydrological and geological process are natural process that also affect water quality but only in small quantity. Hydrology cycle involves the water cycle in hydrosphere which can transfer the pollutant in the atmosphere which then fall with rain water into the soil and water bodies such as river, lake, sea, swap and even groundwater. Geological process involves weathering of igneous and metamorphic rocks that contains chemical elements such as metals, when dissolved in water may change the chemical properties of the particular water, thus lowering the quality of the water. Anthropogenic activities e.g. agriculture, logging and mining are main economic activities in Rompin district (PDT Rompin, 2017). These activities are known sources of heavy metal pollution into the environment and are located near or alongside the river stream in Rompin district.

Heavy metal in river water can accumulate inside the tissue of aquatic organisms whether vertebrate or invertebrate. Various river streams in Rompin district are known for its freshwater prawn source among local and tourist, and are cherished for their unique delicacies taste that different than freshwater prawn from other place. There are two common species of freshwater prawn which is Macrobrachium rosenbergii and Macrobrachium dacqueti, found across the globe including Australia, South East Asia, South America and Africa (Wowor, D., & Ng, P. K. L., 2007). Freshwater prawn found in river in Rompin district belong to Macrobrachium rosenbergii species and can be found either in Rompin or Pontian river during its abundance season. Most of Macrobrachium species are classified as omnivorous with slight carnivorous feeding habit (Lima, Garcia, & Silva, 2014). Feeding rates of M. rosenbergii are affected by pH, temperature, hardness and concentration of heavy metal such as Zn in water they lived in (Satapornvanit, 2006)

1.2 Problem statement

Anthropogenic activities including iron-ore mining in the upstream, logging, paddy field and palm oil plantation alongside the river banks has contribute to the water quality of river in Rompin district, and also of heavy metal pollution (Gasim et al. 2015). In recent years, there has been complaints regarding water quality of Rompin river by the villagers and people who run fish or fresh water prawn business. Two important river in Rompin district are Rompin river and Pontian river, both are crucial as a source for drinking water supply, domestic use, agriculture, and also source of freshwater prawn that become main source of economic activities for certain people. Upstream area of Rompin river are used for water catchment area and source of water supply for water treatment plants. The water flow into these treatment plant come from the area where iron-ore mining is still operational. The downstream area of Rompin river is popular area for fish and freshwater prawn fishing among local and tourist who love fishing as their recreational activity. Pontian river flow from Pontian lake with paddy field and palm oil plantation alongside its river bank. Freshwater prawn or popularly known as ‘udang galah’ is a main attraction for tourist, and it main source come from Rompin river and Pontian river. Accumulation of metals in aquatic organisms were reported by several studies in the past, suggesting that consumption of contaminated food with heavy metal posed risk to human health (Md Kawser Ahmed et al., 2015; Al-Mahaqeri, 2015; Sarkar et al., 2016).

Data collected from surveillance activities from 2014 until 2017 using Water Quality Surveillance (WQS) system showed significant level of heavy metal in Rompin river and Pontian river but are still within permissible limit according to National Drinking Water Standard for raw water. The average concentration of heavy metal in Rompin river were in the order Cd