Screening Tests

The cost of biodegradation testing for registration purposes has increased markedly in recent years and consequently it makes good commercial sense to screen potential compounds before committing to a particular formulation. Naturally one hopes to identify those compounds with the lowest toxicity and highest biodegradability. The biodegradation of test compounds may be evaluated by monitoring a variety of factors. These include: CO₂ evolution, oxygen consumption, removal of dissolved organic carbon, as well as other specific end points. Springborn Smithers Laboratories screens for aerobic and anaerobic biodegradation via a suite of test procedures that are designed to satisfy the requirements of the OECD and FDA and EPA guidelines.

As depicted above, biodegradation can be visualized, and simplified as the growth (metabolism) of an initial population of microorganisms on a substrate (test substance). This is accomplished with either the use of oxygen in aerobic environments, or other electron acceptors in anaerobic environments. Metabolism results in transient biodegradation intermediates, final oxidized (aerobic) or reduced (anaerobic) metabolic products and an increased population of the degrading microorganisms. Simple (ready) biodegradation screening tests generally examine the disappearance of oxygen or dissolved organic carbon and/or the formation of carbon dioxide with relatively dilute microbial populations. Tests can be conducted with or without acclimation of the inoculum to the test substance prior to test initiation. The latter (no acclimation) is a more stringent test and results indicate the extent of "ready biodegradation", i.e., the percent theoretical biodegradation without pre-exposure of the inoculum to the test chemical. Following disappearance of the test substance and the possible formation of transient biodegradation intermediates with specific analytical methods provides additional information from these screening tests. The table below outlines the tests routinely performed by Springborn Smithers.

Species Maintained, Cultured or Used at SPRINGBORN SMITHERS LABORATORIES

Ready Biodegradability
Biodegrad. Screening Test	Test	Biodegrad. Measurement	Water Soluble	Water Insoluble	Volatile	Adsorbing
OECD 301A	DOC Die-Away	DOC	+	-	-	-
OECD 301B	CO2 Evolution	CO2	+	+	-	-
OECD 301D	Closed Bottle	O2	+	+/-	+	+/-
OECD 301E	Modified OECD Screening	DOC	+	-	-	-
OECD 301F	Manometric Respirometry	O2	+	+	-	+
ISO/DIS 14593 OPPTS 835.3120	Sealed Vessel CO2 Production	CO2	+	+	+	+

Tests with Pre-Acclimation
Biodegrad. Screening Test	Test	Biodegrad. Measurement	Water Soluble	Water Insoluble	Volatile	Adsorbing
OPPTS 835.3100	Aerobic Aquatic "Gledhill Test"	CO2	+	+	+	+
FDA 3.11	Aerobic Aquatic	CO2	+	+	+	+
CONCAWE (draft 4/04/96)	Sealed Vessel CO2 Production	CO2	+	+	+	+

Springborn Smithers' highly experienced Environmental Fate Department can provide comprehensive services in support of product registration, effluent management and other more specific requirements as client needs dictate.