Photos of the Long Island Sound

Research & Monitoring


The Long Island Sound Study has launched a new version of the Environmental Indicators section. The data below may be out of date. Please visit and bookmark the new section here to see the most recent data.

Status and Trends: LISS Environmental Indicators

Wastewater Treatment Plants Meeting Toxicity Standards

CTDEEP, Bureau of Water Management

Wastewater Treatment Plants Meeting Toxicity Standards
Percent of CT Plants
1989 76
1990 81
1991 84
1992 85
1993 85
1994 91
1995 91
1996 95
1997 97.9
1998 95.8
1999 94.12
2000 93.6
2001 96.8
2002 96.8
2003 94.7
2004 93.5
2005 97.9
2006 97.8
2007 93.6
2008 95.1
2009 98.8


Aquatic organisms are exposed to effluent from wastewater treatment facilities as a test for effluent toxicity.  Facilities in CT are tested annually and facilities in NY are tested every 5 years.  The data in the chart above represents the percentage of facilities in Connecticut passing these tests.


The toxicity test indicates whether the effluent that is being discharged into Long Island Sound is harmful to aquatic organisms such as fish and invertebrates.  If a wastewater treatment plant fails the test, it is required to make changes to its practices to clean up the effluent that is discharged.


In 2009 only one of 82 Connecticut municipal wastewater treatment plants being tested failed the toxicity test or 1.2%, compared to nearly 25% failure rate in 1989. In Connecticut, a wastewater treatment plant is designated as toxic if it fails 2 consecutive or 3 separate acute tests.

There are 14 New York State facilities discharging into Long Island Sound  whose permits require whole effluent toxicity (WET) testing. The most common requirement is quarterly testing, enabling seasonal effluent characterization, once every five years. For the period 2009-2016 (currently in progress with 1 quarter remaining), all 14 facilities have conducted at least one round of WET testing, with a 100% pass rate to date.

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