How Fish are Exposed to Pesticides

Fish and aquatic animals are exposed to pesticides in three primary ways (1) dermally, direct absorption through the skin by swimming in pesticide-contaminated waters, (2) breathing, by direct uptake of pesticides through the gills during respiration, and (3) orally, by drinking pesticide-contaminated water or feeding on pesticide-contaminated prey. Poisoning by consuming another animal that has been poisoned by a pesticide is termed “secondary poisoning.” For example, fish feeding on dying insects poisoned by insecticides may themselves be killed if the insects they consume contain large quantities of pesticides or their toxic byproducts.

The above is taken from a useful document.

Farming practices are controlled in some countries and less regulated in others. Sales of pesticides are worldwide. Responsible use requires education and understanding of environmental consequences. Some governments lack concerns, economic prosperity is linked to turning a blind eye to often devastating consequences for wildlife and soil health.

.……..any additional phosphorus applied to the land will run off into waterways, where it is a known cause of harmful algal blooms and deoxygenation leading to fish death.

……..as the use of glyphosate increases — the past two decades alone have seen global use increase 15-fold — the herbicide’s relatively small phosphorus content starts to add up, reaching levels comparable to other sources, like detergents, that have attracted regulators’ attention in the past.

This new study argues that the recent and rapid rise in glyphosate use has magnified its relative importance as a source of anthropogenic phosphorus, especially in areas of intensive corn, soybean and cotton cultivation

And from a 2014 article, an awareness of the tiny creatures we are not all aware of that fill the living underwater environment:

Little “Bugs” Can Spread Big Pollution Through Contaminated Rivers

APRIL 10, 2014 —

When we think of natural resources harmed by pesticides, toxic chemicals, and oil spills, most of us probably envision soaring birds or adorable river otters. Some of us may consider creatures below the water’s surface, like the salmon and other fish that the more charismatic animals eat, and that we like to eat ourselves. But it’s rare that we spend much time imagining what contamination means for the smaller organisms that we don’t see, or can’t see without a microscope. The tiny creatures that live in the “benthos”—the mud, sand, and stones at the bottoms of rivers—are called benthic macroinvertebrates. Sometimes mistakenly called “bugs,” the benthic macroinvertebrate community actually includes a variety of animals like snails, clams, and worms, in addition to insects like mayflies, caddisflies, and midges. They play several important roles in an ecosystem. They help cycle and filter nutrients and they are a major food source for fish and other animals. Though we don’t see them often, benthic macroinvertebrates play an extremely important role in river ecosystems. In polluted rivers, such as the lower 10 miles of the Willamette River in Portland, Oregon, these creatures serve as food web pathways for legacy contaminants like PCBs and DDT. Because benthic macroinvertebrates live and feed in close contact with contaminated muck, they are prone to accumulation of contaminants in their bodies. They are, in turn, eaten by predators and it is in this way that contaminants move “up” through the food web to larger, more easily recognizable animals such as sturgeon, mink, and bald eagles. The image below depicts some of the pathways that contaminants follow as they move up through the food web in Oregon’s Portland Harbor. Benthic macroinvertebrates are at the bottom of the food web. They are eaten by larger animals, like salmon, sturgeon, and bass. Those fish are then eaten by birds (like osprey and eagle), mammals (like mink), and people.

An excellent presentation of river wildlife is here. The above illustration is from the pages.

We can all play our part in working toward ensuring our rivers are cherished and all the life that lives within is healthy and untainted.