Pollution load Index

It is indeed no problem to find research topics within the aquatic sciences which are both practically/economically and intellectually/scientifically interesting and relevant. One such research area, which is of increasing significance, concerns the very complicated problem to establish (both quantitatively and qualitatively) ecological effects in the aquatic milieu from various types of contaminants and to develop valid, simple and rapid indicator systems, which may be used with acceptable accuracy in environmental pollution control. There is a growing awareness in the industrialized world today of the necessity of establishing such ecologically valid indicator systems, and although a great deal of research is done within this topic, there is a very large gap between what is done and what should and could be done.

The purpose of this work is to discuss, from a principal point of view, an approach, a model for an ecological risk index to be used in aquatic (limnic) environmental pollution control, i.e. a risk index which provides a fast and simple quantitative value on the potential ecological risk of a given contamination situation in a given lake or fresh water system.

The subsequent model has several limitations and presuppositions which should be stressed already from the very beginning:

The approach concerns only limnic systems.

The desired risk index must of necessity be a crude instrument. However, the philosophy has been that a blunt battle-axe is better than no weapon at all, and in this context it may be appropriate to cite some lines from “Water Quality Criteria” (EPA, 1972, p.179):

“Recommendations

Since forms of species of metals in water may change with shifts in the water quality, and since the toxicity to aquatic life may concurrently change in as yet unpredictable ways, it is recommended that water quality criteria for a given metal be based on the total amount of it in the water, regardless of the chemical state or form of the metal, except that settleable solids should be excluded from the analysis (Standard Methods, 1971).”

To meet the requested demands for accuracy, simplicity and rapidity, the risk index discussed in this context will be based exclusively on sediment data. There are several reasons why a focus on the sediments may be fruitful in this case: (1) data from the sediments provide time-integrated mean values of considerable time-stability compared to data on pollutants from, for example, water samples, (2) sediment samples are comparatively easy to collect in the field, (3) the sample representativity in time and space may be evaluated in a rather simple way, and i4) the adopted analytical procedure can generally provide both cheaper and better data from sediments than from, for example, water samples, because the concentrations are generally much higher in the sediments.

The aim of the approach is that the requested risk index should express the potential ecological risk of a given contamination. The focus is on toxic substances. i.e. substances that give rise to toxic effects on various biological levels (tissue-organ-organism-system), e.g. by disturbing the permeability in the cell membrane, the formation of hormones, or the structure and formation of regulating proteins. Consequently, we will primarily discuss elements like Ag, Be, Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, Se, Sn, V, Zn, substances like polycyclic aromatic hydrocarbons (PAH) and well known environmental poisons like PCB, DDT etc, and will largely avoid nutrient elements (N, P, organic-C), which may influence water quality in quite a different way, which in fact often cancel out, or balance the effect of many toxic substance (metals).

It should also be noted that the desired risk index primarily is intended to express the threat towards man by increased concentrations of toxic substances in fish for consumption. This is easy to say, but in practice as well as in theory, it is very difficult indeed to establish toxicologically valid risk limits.