Autistic disorder (AD) is a severe neurodevelopmental disorder typically identified in early childhood. Both genetic and environmental factors are implicated in its etiology. The number of individuals identified as having autism has increased dramatically in recent years, but whether some proportion of this increase is real is unknown. If real, susceptible populations may have exposure to controllable exogenous stressors. Using literature AD data from long-term (approximately 10-year) studies, we determined cumulative incidence of AD for each cohort within each study. These data for each study were examined for a changepoint year in which the AD cumulative incidence first increased. We used data sets from Denmark, California, Japan, and a worldwide composite of studies. In the Danish, California, and worldwide data sets, we found that an increase in AD cumulative incidence began about 1988-1989. The Japanese study (1988-1996) had AD cumulative incidence increasing continuously, and no changepoint year could be calculated. Although the debate about the nature of increasing autism continues, the potential for this increase to be real and involve exogenous environmental stressors exists. The timing of an increase in autism incidence may help in screening for potential candidate environmental stressors.

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ACKNOWLEDGMENTSThis report was prepared under 3 work assignments of EPA contract #68-C7-0014 to Tetra Tech, Inc. Authors of this report are Jeroen Gerritsen, June Burton, and Michael T. Barbour. We thank Maggie Passmore and Jim Green of EPA Region 3 for helpful guidance, discussions and review. The biological index was made possible by the intensive data collection efforts and discussion of West Virginia DEP; in particular, Janice Smithson, Jeffrey Bailey, Pat Campbell, and John Wirts. This report was prepared with the assistance of Jeffrey White, Erik Leppo, and Brenda Fowler. A Stream Condition Index for West Virginia Wadeable StreamsTetra Tech, Inc. iv March 28, 2000 (Revised July 21, 2000 THIS PAGE LEFT INTENTIONALLY BLANK A Stream Condition Index for West Virginia Wadeable StreamsTetra Tech, Inc. v March 28, 2000 (Revised July 21, 2000 Tetra Tech, Inc. vi March 28, 2000 (Revised July 21, 2000 THIS PAGE INTENTIONALLY LEFT BLANK A Stream Condition Index for West Virginia Wadeable StreamsTetra Tech, Inc. vii March 28, 2000 (Revised July 21, 2000 LIST OF FIGURES Tech, Inc. viii March 28, 2000 (Revised July 21, 2000 LIST OF TABLES EXECUTIVE SUMMARYOver the past century, land use activities such as mining, agriculture, urbanization, and industrialization have seriously threatened the quality of surface waters by contributing to nonpoint-source pollution. In West Virginia, the investigation of these nonpoint sources of water pollution has become a priority. indicator of ecosystem health and can identify impairment with respect to the reference (or natural) condition. The index includes six biological attributes, called metrics, that represent elements of the structure and function of the bottom-dwelling macroinvertebrate assemblage. Metrics are specific measures of diversity, composition, and tolerance to pollution, that include ecological information.The SCI is to be used as the basis for bioassessment in West Virginia and has been calibrated for a long-term biological index period extending from April through October. A data analysis application has been developed to ensure consistency in data management and analysis throughout the state as DEP biologists conduct biological monitoring.Benefits expected from the implementation of the WV SCI will apply to a broad spectrum of management programs, including:characterizing the existence and severity of point and nonpoint source impairment;targeting and prioritizing watersheds and ecosystem management areas for remedial or preventive programs; evaluating the effectiveness of nonpoint source best management programs; screening ecosystems for use attainability; and developing a basis for establishing biocriteria that relate to regional water quality goals, an EPA priority.The West Virginia SCI was tested with independent data collected in 1998 and was able to correctly identify the majority of the stream sites stressed in some way by human disturbance or pollution. Index scores were divided into 5 proposed rating categories for reporting on the condition...