Photos of the Long Island Sound

Status and Trends: LISS Environmental Indicators

Type of Indicators: Health/Condition Response/Performance Socio-Economic Historical/Background

Wastewater Treatment Plants Meeting Toxicity Standards

Source: 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

What are Toxicity Standards?

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.

What does this indicate?

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 11 New York State facilities discharging into Long Island Sound  whose permits require whole effluent toxicity (WET) testing. In NY, treatment plants are tested in a five year cycle. For the period 2006 – 2008, four wastewater treatment plants were required to conduct WET testing. Two of these facilities failed and required continuous testing.

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