The NCASI ecological assessment program seeks to understand the compatibility of pulp mill effluents with healthy receiving water aquatic ecosystems. NCASI staff biologists and sponsored researchers at universities conduct research that addresses numerous aspects of this relationship. Measuring responses of organisms exposed to pulp mill effluents  during  whole  effluent toxicity  tests, and determining factors responsible for any responses, is an important part of the program.   The role nutrients in pulp mill effluents may play with respect to in-stream biota is also being investigated. The work follows and documents the significant changes in aquatic ecosystem responses brought about by pulp and paper mill process changes and effluent treatment system improvements.

Aquatic biology investigations at NCASI fall into three categories. The first two relate to the specific question of whether pulp mill effluents may influence the reproduction processes of fish in receiving waters, and address the possible role of endocrine disruption mechanisms. Studies addressing morphological changes in native Gambusia species show that concerns about anal fin elongations are significantly reduced following process improvements at pulp mills. Research using life-cycle assays with fathead minnows, an EPA test species, likewise shows that potential reproductive effects are lessened or totally removed with process improvements such as controlling loss of pulping liquors.

NCASI is also conducting Long-Term Receiving Water Studies unique in the history of aquatic ecosystem investigations. Four U.S. rivers receiving treated effluent discharge from a modern pulp and paper mill are included. Monitoring sites are established at locations upstream and downstream of the discharge, in some cases for over 30 miles, so that gradient effects may be observed if present. At each monitoring site, samples are collected at least twice yearly for analysis of periphyton, macroinvertebrates, and fish populations, in addition to studies of water quality, effluent quality, and habitat condition. The sample collection and data analyses began in 1999, and the studies are expected to span 10 to 20 years. A Science Advisory Panel of international experts in aquatic ecosystem assessment guides the work. Researchers have developed and published new insights into the methodology of large-scale receiving waters characterization, as well as methods for risk assessment associated with such studies. Coupled with multivariate statistical data analysis and ancillary relative risk assessment studies, the data indicate that the pulp mill effluents have minimal, if any, influence on the receiving-water communities.

Results of these investigations are provided in NCASI reports, in presentations at scientific meetings, and in publications in the peer-reviewed scientific literature.