Making Year-to-Year Comparisons of TRI Data

Year-to-year comparisons must be based on a consistent set of reporting requirements to assure that any changes in the data do not simply reflect expansion of TRI's chemical and industry coverage or other modifications in reporting requirements over the course of the years. Therefore, trend analyses have been undertaken using various baseline years, as described below. Chemicals that have been removed from the TRI list ("delisted" chemicals) are excluded from all of the year-to-year comparisons.

2000-2006
For 2000, EPA made changes to the list of chemicals that must be reported and to reporting thresholds for some chemicals. EPA has the authority both to add chemicals to the TRI reporting list if they meet the statutory toxicity criteria and to delete chemicals from the list if EPA determines that they do not meet the toxicity criteria. For the 2000 reporting year, PBT chemicals already on the list had the reporting thresholds lowered and other PBT chemicals were added to the list. In addition, vanadium compounds were added to the list and the qualifier for vanadium was changed to exclude vanadium when contained in alloys starting with the reporting year 2000. These chemicals are included for analyses covering the 2000-2006 period, but not for periods covering years prior to 2000. The reporting thresholds for the PBTs lead and lead compounds were lowered starting with the reporting year 2001. Lead and lead compounds are not included for analyses covering the 2000-2006 period or for periods covering years prior to 2001.

Additional considerations also apply to analyses of TRI data for 2000-2006. Beginning with reporting year 2002, amounts sent off-site to landfills/disposal surface impoundments are reported in three separate categories (RCRA Subtitle C landfills, other landfills, and surface impoundments). These types of transfers to disposal or other releases cannot be analyzed separately for years prior to 2002.

1998-2006
Chemicals whose reporting requirements changed starting with the 2000 or 2001 reporting year (see above) are excluded for analyses covering the 1998-2006 period. Seven industry sectors were required to report starting with the 1998 reporting year, including metal mining, coal mining, electric utilities, chemical wholesale distributors, petroleum bulk storage/terminals, hazardous waste management facilities and solvent recovery facilities. These industries are included for analyses covering the 1998-2006 period, but not for periods covering years prior to 1998.

1995-2006
Chemicals added to TRI in EPA's chemical expansion initiative were first reportable in 1995. These chemicals are included for analyses covering the 1995-2006 period, but not for periods covering years prior to 1995. PBT chemicals whose reporting requirements changed starting with the 2000 or 2001 reporting year (see above) are excluded for analyses covering the 1995-2006 period. Since 1995, EPA has deleted three chemicals from the TRI list, including phosphoric acid in 1999. These chemicals are excluded from all analyses of multi-year data. Also, reporting by the seven industries added to the TRI starting with the 1998 reporting year is excluded from the 1998 through 2006 data for analyses covering the 1995-2006 period.

Additional considerations also apply to analyses of TRI data for 1995 to 2006: Beginning with reporting year 1996, the amounts injected underground into Class I wells are reported separately from amounts injected into underground wells of other classes (II-V), and on-site land disposal in RCRA Subtitle C landfills separately from other types of on-site landfills. These types of disposal or other releases cannot be analyzed separately for years prior to 1996.

1991-2006
Reporting requirements for ammonia, hydrochloric acid, and sulfuric acid have changed since 1991. Analyses for the period 1991-2006 exclude chemicals added to TRI since 1991 and those for which reporting requirements have changed over that time. Also, reporting by the seven industries added to the TRI starting with the 1998 reporting year is excluded from the 1998 through 2006 data for analyses covering the 1991-2006 period.

Waste management information added to TRI by the Pollution Prevention Act of 1990 has been collected since 1991. In addition, reporting on off-site transfers to recycling and on off-site transfers to energy recovery were added in 1991. Therefore, waste quantity reports are available only for analyses covering the years 1991-2006, but not for periods covering years prior to 1991. Also, waste transfer reports that include transfers to recycling and energy recovery are available for analyses covering years 1991-2006, but not for periods covering years prior to 1991.

1988-2006
Analyses for the period 1988 to 2006 exclude chemicals added to TRI since 1988 and those for which reporting requirements have changed over that time. This includes chemicals described above as well as aluminum oxide whose qualifier changed to "fibrous forms" for the 1989 reporting year. Also, reporting by industries required to report starting with the 1998 reporting year is excluded from the 1998 through 2006 data for analyses covering the 1988-2006 period.

Waste management information added to TRI by the Pollution Prevention Act of 1990 has been collected since 1991. In addition, reporting on off-site transfers to recycling and on off-site transfers to energy recovery were added in 1991. Therefore, waste quantity reports are not available for analyses covering the years 1988-2006, and waste transfer reports do not include transfers to recycling and energy recovery for analyses covering the years 1988-2006.