Introduction:
Bioaccumulation is a process by which the concentration of a chemical increase over time in a biological organism compared to the chemical's concentration in the environment. Compounds accumulate in living things any time they are taken up and stored faster than they are broken down (metabolized) or excreted.
Now the question is why do we care about bioaccumulation? The reason we do care about bioaccumulation is those chemicals are accumulate in human body through different path ways (for details, see Appendix A). In my research, the contaminated chemical that I am focusing on is PCBs (Polychlorinated Biphenyl). It is a category or family of chemical compound formed by the addition of chlorine to biphenyl. They have been shown to cause cancer, brain damage, and liver defects in humans. Even though the use of PCBs has been prohibited since 1977, existing PCBs continue to pose a problem, finding various pathways to travel through the ecosystem to humans.
Bioconcentration Factor:
Understanding the dynamic process of bioaccumulation is very important in protecting human beings and other organisms from the adverse effects of chemical exposure, and it has become a critical consideration in the regulation of chemicals and bioconcentration factor. Determination of the BCF (Bioaccumulation Factor) is extremely important in the risk analysis of a compound (PCBs).
BCF (L/wet weight of fish) = ( ν fish)/(C dis)
Here, ν fish = (μg PCB/g wet)
C dis = (dissolved chemical concentration)
Biomagnification:
We humans are at the top of food chain and being on top does have some disadvantages. Before 1977 a lot of industries, manufactures, chemical labs etc. used to discharge a lot of chemical including PCBs. Although the U.S. banned production of PCBs in 1977, the contaminated sediments in Rivers and Harbor floors continue to act as a reservoir from which PCBs enter the food chain, with humans standing at a very critical and dangerous position at the top.
Although this position appears to be farthest from harm, it is potentially the most dangerous and severely affected due to a process known as "Biomagnification" that results in bioaccumulation. Biomagnification is the process by which PCB concentrations or levels bioaccumulate, or increase in the consumer at each step of the food chain.
An overview of food chain:
The PCB food chain begins when PCBs bind to sediment particles suspended in water and eventually settle to the rivers, streams, estuaries, or lake-bottom where they accumulate. These contaminated sediments eventually mix into the bottom mud during turbulence created by storms, river currents, and passing boats. The result is toxic sludge.
Other sediments may cover this toxic sludge, but it still remains easily accessible to sediment-digging organisms that burrow into the contaminated material. These "benthic," or bottom-dwelling, organisms are tiny animals, such as mayfly and dragonfly larvae, that live in sediments. As they burrow, benthic organisms absorb PCBs. This begins the biomagnification process. In the following food chain, it is shown clearly.
(Sustainable Resources Development, Alberta Government)
Fishes that are low on the food chain eat these benthic organisms, along with the PCBs they absorbed. Consumption and digestion are the primary means of exposure to and bioaccumulation of PCBs. For example, walleye have higher levels of PCBs than perch because they eat perch and absorb PCBs with every contaminated fish they eat. Therefore, even sediment barely contaminated with PCBs can result in high concentrations in both water and land-based life, including humans. Moreover, PCBs have a high affinity for organic substances, such as fat molecules. In other words, PCBs accumulate in fat, making women, who on average have a higher body-fat content than men, and the children they bear more vulnerable to these toxic substances.
Continuing my research:
In order to analyze the Bioaccumulation of PCB, I am using a computer model. The Bioaccumulation Model has been provided by Kevin J. Farley, Manhattan College. This computer model calculates the concentration PCBs in fishes. In order to analyze the total scenario, I have collected some raw data of different contaminated fishes in different years. Those raw data has been provided by Larry Skinner, New York State Department of Conversation. My objective is to compare and contrast between the computer model and the real raw data and come up with some new ideas. This research is to be continued.
Appendix A:
- The highlighted line shows the major path way of PCBs.
Figure 1: A Flow Chart of Bioaccumulation Pathway.