Ecotoxic properties

Oxime carbamates are generally applied either directly to the tilled soil or sprayed on crops. One of the advantages of oxime carbamates is their short persistence on plants. They are readily degraded into their metabolites shortly after application. However, some of these metabolites have insecticidal properties even more potent than those of the parent compound. For example, the oxidative product of aldicarb is aldicarb sulfoxide, which is observed to be 10-20 times more active as a cholinesterase inhibitor than aldicarb. Other oxime carbamates (e.g., methomyl) have degradates which show no insecticidal activity, have low to negligible ecotoxicity and mammalian toxicity relative to the parent, and are normally nondetectable in crops. Therefore, the residue definition may include the parent oxime carbamate (e.g., methomyl) or parent and metabolites (e.g., aldicarb and its sulfoxide and sulfone metabolites). The tolerance or maximum residue limit (MRL) of pesticides on any food commodity is based on the highest residue concentration detected on mature crops at harvest or the LOQ of the method submitted for enforcement purposes if no detectable residues are found. For example, the tolerances of methomyl in US food commodities range from 0.1 to 6 mg kg for food items and up to 40 mg kg for feed items. ... 

As mentioned above, there are characterization factors for a number of different impact categories, e.g. acidification, eutrophication, climate change, human toxicity and ecotoxicity. However, characterization factors are missing for many additives, especially for human toxicity and ecotoxicity, which makes it difficult to assess the potential impact that a product will cause during its entire life cycle. A major reason that characterization factors are often missing is the lack of data regarding substance properties, such as physical chemical properties and toxicity. 

In a study by Andersson et al. [30], the possibilities to use quantitative structure-activity relationship (QSAR) models to predict physical chemical and ecotoxico-logical properties of approximately 200 different plastic additives have been assessed. Physical chemical properties were predicted with the U.S. Environmental Protection Agency Estimation Program Interface (EPI) Suite, Version 3.20. Aquatic ecotoxicity data were calculated by QSAR models in the Toxicity Estimation Software Tool (T.E.S.T.), version 3.3, from U.S. Environmental Protection Agency, as described by Rahmberg et al. [31]. To evaluate the applicability of the QSAR-based characterization factors, they were compared to experiment-based characterization factors for the same substances taken from the USEtox organics database [32], This was done for 39 plastic additives for which experiment-based characterization factors were already available. 

The Danish (Q)SAR database is a repository of estimates from over 70 [28] (Q)SAR models for 166,072 chemicals. The (Q)SAR models encompass endpoints for physicochemical properties, fate, ecotoxicity, absorption, metabolism, and toxicity... 

A case can often be made to omit studies as scientifically unnecessary, because it is possible to conduct an adequate risk assessment without them. This is most often the case if the substance decomposes to degradants of known hazardous properties. For example the substance may hydrolyse rapidly to non-toxic products, so the key issue is to establish that this happens rapidly in the stomach before the parent substance can be absorbed. There may then be a case for omitting the expensive long-term animal studies, providing it is also established that there is no dermal or inhalation absorption from these exposure routes. In a similar way, it may be justified to omit ecotoxicity studies on a substance which hydrolyses or otherwise decomposes in the aquatic environment to stable products that have already been tested. 

Potentially it may be useful to have an expert report to collect, summarise and evaluate all the available literature data and in-house studies to get an overall view of the toxicity, environmental fate or ecotoxicity of a substance. A simple expert report would be on a single hazardous property, such as toxicokinetics or long-term general toxicity, and in effect would be a review article. 

The first problem in interpretation of the probable ecotoxicity of a given chemical is selecting those species and possible effects, which are most significant (Duffus, 1986). This requires a knowledge of ecosystems at risk together with an ability to assess the likely toxicity of the chemical from its chemical and physical properties and mammalian effect data that are usually available. 

This screening of physical/chemical properties that relate to pharmacokinetics is already widely used within the pharmaceutical industry [105]. The current methodology can easily be expanded to include properties relating to environmental fate and ecotoxicity. 

In the GSK approach, each factor was given a score based on available physical property data (for example boiling point), life cycle impact data, or experimentally derived data (such as animal toxicity or ecotoxicity data). Related factors were associated together before the combined data was normalized between 1 (worst) and 10 (best) to give final scores for the headline categories (incineration, ecotoxic-ify, exposure potential, and so on). This approach enabled the envirorunental and health and safety properties of solvents of different types or classes to be easily compared alongside more conventional physical and solvent properties. In an ideal world, a similar approach would be taken with every single chemical to be able to... 

Staples, C.A. and Davis, J.W. (2002) An examination of the physical properties, fate, ecotoxicity and potential environmental risks for a series of propylene glycol ethers, Chemosphere 49 (1), 61-73. 

As of 1981, when theEuropeanchemicalspolicy was implemented, theEuropean Union required the submission of base set test data for physiochemical, environmental fate, toxicological properties and health effects, and ecotoxicity parameters for new... 

Ecotoxicity The property of a compound to produce adverse effects in an ecosystem or one of its components. 

Saarikoski, J., Viluksela, M. (1982) Relation between physicochemical properties of phenols and their toxicity and accumulation in fish. Ecotox. Environ. Saf. 6, 501-512. 

EC, 1992. EC A.8. Partition coefficient. Annex V (Directive 67/548/EEC). Methods for determination of physico-chemical properties, toxicity and ecotoxicity... 

The OECD Guidelines for the Testing of Chemicals is a collection of standard methods used by professionals in governments, industry, academic institutions, and independent laboratories for safety testing of chemical substances. They cover tests for physical-chemical properties, effects on biotic systems (ecotoxicity), environmental fate (degradation/ accumulation), and health effects (toxicity) (see Table 1). The Test Guidelines are systematically updated to respond to scientific progress or to address new needs identified by member countries. They are published in two loose-leaf binders, and are also available in a CD-ROM version. 

Lynch DG, Tirado NF, Boethhng RS, Huse GR, Thom GC. Performance of online chemical property estimation methods with TSCA premanufacture notice chemicals. Ecotox Environ Safety 1991 22 240-9. 

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