What are the Human Health Effects of Pesticides?

Bioaccumulation (or bioconcentration):
Is the increase in concentration of a pollutant from the environment to the first organism in a food chain
Is the movement of a chemical from the surrounding medium into an organism – the primary “sink” for some pesticides is fatty tissue or “lipids”) .
Biomagnification:
Is the increase in concentration of a pollutant from one link in a food chain to another
Describes the increasing concentration of a chemical as food energy is transformed within the food chain. As smaller organisms are eaten by larger organisms, the concentration of pesticides and other chemicals are increasingly magnified in tissue and other organs. Very high concentrations can be observed in top predators, including man

In Bioaccumulation:
The level at which a substance accumulates depends on the rate of uptake (eg: through the gills of a fish, contact with the skin)
How quickly the substance is removed, depends on the metabolic process, the lipid content of the organism and other environmental and physical factors
The more hydrophobic a substance is the more likely it is to bioaccumulate
If the pesticide level within an animal is high enough it can kill the animal
The pesticide is passed on to other organisms when the ones with pesticides contained in the fatty tissues are eaten (biomagnification)
The concentration of the pesticide is then increased as a predator will eat numerous of the prey

In order for biomagnification to occur, the pollutant must be:

• long-lived
• mobile
• soluble in fats
• biologically active

If a pollutant is short-lived, it will be broken down before it can become dangerous.  If it is not mobile, it will stay in one place and is unlikely to be taken up by organisms.  If the pollutant is soluble in water it will be excreted by the organism. Pollutants that dissolve in fats, however, may be retained for a long time.

Classic Example of Biomagnification: how DDT gets magnified as it passes through a food chain

[singlepic id=226 w=320 h=240 float=center]
The figure shows how DDT becomes concentrated in the tissues of organisms representing four successive trophic levels in a food chain.

The concentration effect occurs because DDT is metabolized and excreted much more slowly than the nutrients that are passed from one trophic level to the next. So DDT accumulates in the bodies (especially in fat). Thus most of the DDT ingested as part of gross production is still present in the net production that remains at that trophic level.
This is why the hazard of DDT to nontarget animals is particularly acute for those species living at the top of food chains.

For example,
spraying a marsh to control mosquitoes will cause trace amounts of DDT to accumulate in the cells of microscopic aquatic organisms, the plankton, in the marsh.
In feeding on the plankton, filter-feeders, like clams and some fish, harvest DDT as well as food. (Concentrations of DDT 10 times greater than those in the plankton have been measured in clams.)
The process of concentration goes right on up the food chain from one trophic level to the next. Gulls, which feed on clams, may accumulate DDT to 40 or more times the concentration in their prey. This represents a 400-fold increase in concentration along the length of this short food chain.
There is abundant evidence that some carnivores at the ends of longer food chains (e.g. ospreys, pelicans, falcons, and eagles) suffered serious declines in fecundity and hence in population size because of this phenomenon in the years before use of DDT was banned (1972) in the United States.

Effects at the organism or ecological level are usually considered to be an early warning indicator of potential human health impacts.

More reading.

Related posts:

1. What are Pesticides, and How are They Absorbed in Our Environment