Effects of atrazine runoff on Chesapeake Bay aquatic life: Risk assessment of atrazine on the blue crab

Russell F. Ford

David Lucero

Henrietta Oakley

Satish Serchan

Executive Summary
Atrazine is the most extensively used herbicide for control of weeds in agricultural crops in the United States (EPA, 2003), with an estimated annual production of 76 million pounds (Hayes et al., 2003). Atrazine is frequently detected in surface waters and has been known to affect reproduction of aquatic flora and fauna, changing the community structure as a whole (Stagnitti et al., 2001). Due to negative impacts on aquatic life, it has been banned in the European Union.

In the Chesapeake Bay area, declines in abundance and health in submerged aquatic vegetation have been linked to increase atrazine use around the Bay resulting in an overall decline in the fish and waterfowl productivity (Christopher et al., 1992). Blue crabs (Callinectes sapidus) are an ecological indicator for the Bay and play large roles in energy transfer from estuaries to the nutrient limited ocean environment. Blue crabs play an important role in controlling the trophic cascades within an estuary. Blue crab populations do not flourish in watersheds associated with agricultural land use and pollution (King et al., 2005). Atrazine reduces chlorophyll-a within primary producers, prohibiting photosynthesis and cell division in certain species of submerged aquatic vegetation and phytoplankton important for the survival of the blue crab.

Exposures to concentrations as low as 0.1 part per billion of atrazine in surface water adversely affects frogs by causing the male frog gonads to produce eggs – effectively turning males into hermaphrodites (Hayes et al., 2003). These effects have been shown in controlled laboratory studies as well as in the wild. Elevated rates of human prostate cancer have been shown in some studies of workplace exposure. Atrazine may act on amphibians by stimulating production of aromatase, an enzyme that is linked to the growth of cancers in humans.

This report finds reasons for concern over the possible impacts of atrazine runoff on the Chesapeake Bay’s flora and fauna. In addition, this report presents direct and indirect impacts of atrazine on the blue crab’s habitat and food sources. This report also highlights the adverse effects of atrazine on frogs and human health. The information can be used for developing management guidelines and legislation.

Atrazine is a common non-point source pollutant in runoff entering the Chesapeake Bay, and is suspected of contributing to the decline of blue crab populations.

The safety of atrazine in the environment has been the subject of recent review by the Unisted States Environmental Protection Agency and legal action by the Natural Resource Defense Council. Numerous studies address the impact of atrazine on individual components of the Chesapeake Bay ecosystem, but none of which we are aware, addresses possible impacts at the system level. The Chesapeake Bay is already heavily impacted by the agricultural lands found within its watershed threatening the health of the ecosystem and the viability of its fisheries.

This report will discuss literature relevant to possible impacts of atrazine runoff on the Chesapeake Bay estuary, including sub-aquatic vegetation (SAV), phytoplankton, and fauna dependent on these primary producers, particularly blue crabs (Callinectes sapidus). The role of the chemical as an endocrine disrupter in amphibians and humans will also be assessed.

An investigation of the presence and sources of atrazine in the Chesapeake Bay watershed will be conducted through a review of the pertinent literature. A broad range of studies will be identified that exemplify deleterious non-target impacts of the herbicide. The current review by the US EPA on the safety of atrazine, will be the basis for the argument against the safety of atrazine, and the attempt to model the effects of the pesticide on aquatic ecosystems will link cause and effect to the blue crab. Evidence of endocrine disruption and abnormal sexual development in amphibians due to exposure to atrazine will be used to argue that there is larger threat than what has currently been identified. This will show that the direct effects of atrazine exposure has undergone little research, though this endocrine conversion pathway is shared with humans and other mammals, and may linked to increased cancer rates in humans.

The Chesapeake Bay watershed stretches across more than 64,000 square miles, is home to 136 million people (Burke et al., 2000), and encompasses parts of six states and the District of Columbia [Figure 1]. The Chesapeake Bay is historically an important source of fish and shellfish, with a large industry based on the blue crab.

Figure 3: Molecular structure of atrazine (Stagnitti et al., 2001).