**1.1 Physicochemical problems and emergences of biomonitoring**

Common methods that rely on chemicals to monitor river pollution are increasingly suitable for monitoring systems as they can detect physical and environmental pressures occurring over time and on multiple scales [1–5]. However, concepts, and

principles of biomonitoring, which are more efficient and effective than traditional methods, have been developed and widely used worldwide to monitor river pollution. Compared to common and uncommon species, bioindicators are more tolerant to environmental change. They are sensitive enough to detect environmental change thanks to their tolerance, but they are also resilient enough to deal with some variability and represent the overall biotic response [6]. However, this new initiative has liberated tropical areas by allowing the model and adaptation of current geologically developed non-tropical species using natural freshwater organisms. These biomonitoring indicators are often developed for specific regions to respond to regional variables using local biotic collections that reflect regional variability based on sensitivity or biological tolerance. Such variations may affect the strength, performance, and reliability of biomonitoring indicators developed in non-tropical areas (mean temperature between 21 and 30°C and rainfall 100 inches a year) when used in tropical rivers (mean temperatures above 18°C and monsoonal patterns rainfall 79 to 394 inches) [7]. Similarly, modification of non-thermal bio-monitoring indicators used in tropical areas is often captured by incomplete taxonomical resolution and unknown levels of tropical taxa [4]. Abiotic variables or physiochemical samples are problematic in identifying a change or impact in some environmental conditions. For example, contamination can be present in toxic quantities or bio-accumulated, which causes adverse biological deterioration. However, contaminated concentrations may be too small to be detected using this procedure [8]. Consequently, changes in behavioral or pathological responses, population dynamics, environmental pollution, and impacts have been measured using biological rather than physic-chemical indicators by many scientists because of the direct interaction of an organism with the ecosystem [9–11].
