Who is phasing out what

Volunteer Image Author TheDigitalArtist

The world is phasing out fossil-fuels, old polluting vehicles, plastic products, toxic substances, nuclear power, biofuel, incandescent light bulbs, ozone depleting substances, waste imports, second hand clothes, food waste, and ivory trade. These are either gradual phase outs or immediate bans. So, who exactly is phasing out what? Read ahead to find out.

Who is phasing out fossil-fuels?

Who is phasing out old polluting vehicles?

Who is phasing out plastic products?

Who is phasing out toxic substances?

Who is phasing out nuclear power?

Who is phasing out biofuel?

Who is phasing out incandescent light bulbs?

Who is phasing out ozone depleting substances?

Who is phasing out waste imports?

Who is phasing out second hand clothes?

Who is phasing out ivory trade?

 Who is banning food waste?

Who is banning deforestation?

Last Edited: April 4 2018


Volunteer image author Kangheungbo

Isosteres are substances with similar molecular and electronic characteristics. They may not be structurally related, but they often have similar physical properties. They are chemical substances, atoms or substituents that possess nearly equal or similar molecular shape and volume, approximately the same distribution of electrons and which exhibit similar chemical properties. Benzene and pyridine are classical examples of isosteres.

Can a carcinogenic molecule be made safe by knowing its isostere ? Yes. Look at this for example.


Does it mean all F isosteric substitutions are safe?

Isosteres -2

Does it depend on the position?

Isosteres -3

Silicon as an isostere for Carbon:

Si is the 2nd most abundant element on the planet. Naturally occurring Si-C bonds are unknown. Even if they were, such bonds must have immediately formed some other bond.

Silicon substitution in acetylcholine analogs:

Isosteres -4

Acetylcholine is a neurotransmitter. A muscarinic receptor agonist is an agent that enhances the activity of muscarinic acetylcholine receptor.

Silane analogue of Polyethylene, Air stable:

Isosteres - 5

In the presence of water and/or soil, siloxanes hydrolyze to smaller oligomers and monomeric 1,1-dimethylsilanediol.


Mammals also rapidly oxidize silicon-hydrogen bond, whereas the carbons attached to silicon are metabolized much like simple hydrocarbons.


DDT, DDD & Silicon isosteres:


DDT  = dichlorodiphenyltrichloroethane

DDD = dichlorodiphenyldichloroethane

Why is DDT good? Millions of lives were saved against mosquitoes with the help of it. Why is DDT bad? It turned out to be an endocrine disruptor, genetoxic, persistent and exteremely hydrophobic chemical.

Insecticide MTI-800:


If you replace C with Si, no mortality of fish is observed at 50 mg/l. While with C in it, Fish LD50 is 3 mg/l.

Further reading:

Last edited: December 19th 2017

Designing a safer chemical

Volunteer image author Eswamy

Here are some strategies for safer chemical design:

  1. Reduce absorption
  2. Use of toxicity generating mechanism
  3. Use of structure activity (toxicity) relationships
  4. Use of isosteric replacements
  5. Use of retrometabolic (‘soft’ chemical) design
  6. Identification of equally efficacious less toxic chemical substitutes of another class
  7. Elimination for the need for associated toxic substances

While considering these aspects, it is best to dividethem into two categories, namely external considerations and internal considerations.

External considerations:

Reduction of exposure or accesiblity:

Properties related to environmental distribution/dispersion:

  • Volatility, density, melting point. For example, Carbon disulphide is stored in pool of water because it is denser than water. Also, petrol/diesel are stored underground to keep the temperature low.
  • Water solubility.
  • Persistence/Biodegradation: Oxisdation, hydrolysis, photolysis, microbial degradation. These are all related to structural stability.
  • Conversion to biologically active substances.
  • Conversion to biologically inactive substances.

Properties related to uptake by organisms:

  • Volatility
  • Lipophilicity
  • Molecular size
  • Degradation: Hydrolysis, effect of pH, susceptibility to digestive enzymes.

Consideration of routes of absorption by mass, animals or aquatic life:

  • Skin/eyes
  • Lungs
  • GI tract
  • Gills or other species-specific routes

Reduction/elimination of impurities:

  • Generation of impurities of different classes
  • Presence of toxic homologues
  • Presence of toxic, geometric, conformational or stereoisomers.

Internal considerations:

Facilitation of detoxication:

  • Facilitation of excretion: Selection of hydrophilic compounds, facilitation of conjugation/acetylation
  • Facilitation of biodegradation: Oxidation, reduction, hydrolysis.

Avoidance of Direct Toxication:

  • Selection of chemical class or parent compound
  • Selection of functional groups: Avoidance of toxic groups, planned biochemical elimination of toxic structure.
  • Structural blocking of toxic grouos
  • Alternative molecular sites for toxic groups

Avoidance of Indirect Biotoxication (Bioactivation):

  • Addressing Bioactivation: Avoiding chemicals with known activation routes – (1) highly electrophilic or nucleophilic groups (2) unsaturated bonds (3) other structural features
  • Structural blocking of bioactivation

You must already be familiar with isosteres by now. Here are some other ways to deal with toxic substances.

Use of Retrometabolic (Soft Chemical) Design:

A ‘soft’ chemical can be defined like soft drugs. A substance deliberatly designed such that it contains the structural features necessary to fulfill its commercial purpose but if absorbed into exposed individuals, it will break down quickly and non-oxidatively to non-toxic readily excretable substances. For example, safer alkylating agents and safer analog of DDT.

Equally efficacious, less toxic substitutes of another class:

Focus on commercial application and depends on the successful identification of a less toxic substance of a different chemical class.


  1. Acetoacetate as substitutes for isocyanates in sealants and adhesives
  2. Isothiazoles as substitutes for organotin anti-foulants
  3. Sulfonated diaminobenzanilides for benzalidines in dyes

Elimination of associated toxic substances:

The subtance per se is not toxic but its storage, transportation or use may require an associated substance which is toxic. For example, solvent replacement.


  1. Water based paints instead of oil based paints
  2. Supercritical CO2 for organic solvents
  3. Dibasic esters (e.g. methyl esters of adipic, succinic acid and glutaric acids) to replace glycol ethers, cyclohexanone, isophorone, cresylic acid, methylene chloride and others)

Cetylpyridinium chloride and its soft analog:

Cetylpyridinium chloride (CPC) is a cationic quaternary ammonium compound in some types of mouthwashes, toothpastes, lozenges, throat sprays, breath sprays, and nasal sprays. Cetylpyridinium chloride is present in commercial products listed in this Wikipedia article.

IMG-1461 (1)

Acetoacetate based sealants and adhesives:


Carcinogenicity of Aromatic Amines:

Simplest of these systems is Aniline. The unattached bonds on these ring systems indicate the positions where attachment of amines or amine generating group(s) gives rise to carcinogenic compounds.

Let’s look at the molecular design of aromatic amine dyes with lower carcinogenic potential. Find it here: OncoLogic™ – The Cancer Expert System – An Overview

Last edited: December 19th 2017

Life-Cycle Analysis/Assessment (LCA)

Volunteer image author Jarmoluk

LCA is a technique used for assessing the environmental aspects and potential impacts associated with a product by:

  • compiling an inventory of relevant inputs and outputs of a product system
  • evaluating the potential environmental impacts associated with those inputs and outputs
  • interpreting the results

It is a method in which the energy and the raw material consumption, different types of emissions and other important factors are being measures, analysed and summoned over the product’s entire life cycle from an environmental point of view.

It is a ‘Cradle to Grave’ approach. It started in the early 1970s and initially analysed only energy requirements.

While USA has its own standards, Europe and Japan follow international standards. ISO 14040-14043 is considered to be the LCA standard.

  • Raw material aquisition (Material extraction) : For example, extraction of air/water/minerals/crude oil etc.
  • Material manufacturing (Material processing): For example, modification of the extracted product, say Fe to steel.
  • Product manufacture: For example, Making of a car.
  • Use (Produce use, maintenance, upgrade): For example, using the car.

LCA approach in based on the following four steps:

  1. Goal definition (ISO 14040): The basic and scope of the evaluation are defined.
  2. Inventory Analysis ( ISO 14041): Complete mass and energy balance.
  3. Impact Assessment (ISO 14042)
  4. Improvement Assessment (ISO 14043)

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Last edited: December 19th 2017


Some mushrooms are known to be edible whereas some are toxic. Volunteer image author Adege.

Toxicology helps us design processes using safer chemicals. It’s not just us who we have to think of, but all other species on the planet that are affected by anthropogenic processes. By studying how a certain chemical affects us and other species, we can make better decisions. There are a few aspects which we need to consider to learn about the toxic effects of chemicals on all of us.

  • Should a chemical be banned?
  • What is a drug?
  • What is a poison?
  • What is a toxin?
  • What is a dose?
  • What is exposure?
  • Means of administration?
  • Understand the difference between Pharmacology and toxicology: Pharmacology is the scientific study of the origin, nature, chemistry, effects and use of drugs. Toxicology is the science that investigates the adverse effects of chemicals on health.


“The right dose differentiates a poison and a remedy.”  -Paracelsus

To explain this quote by Paracelsus, an Ayurvedic medicine called ‘Makardhwaj’ is a perfect example. Makardhwaj contains mercury. In the right quantities, it proves to be a medicine and not a toxin.

To calculate dose we use the following formula: Dose (in ppm)= (gm of chemical)/(kg of body weight)

Knowing the dose is insufficient and serves only as the starting point. We also need to know the following things:

  • Environmental concentration
  • Properties of toxicant
  • Frequency of exposure
  • Length of exposure
  • Exposure pathway

Response to drugs/toxins varies individually.

Distribution, metabolism and excretion

Distribution, metabolism and excretion describe what happens to the drug or toxin in the body

  • Distribution: Organs that are reacted
  • Metabolism: Chemical transformation – metabolites
  • Excretion: Elimination

Did you know? If you are exposed to a certain amount of amine, you won’t be able to sleep for three days. Also, if you put your hand in Carbon Tetrachloride for 30 min, it can be fatal. Did you also know if you drink 5 litres of milk everyday, you will probably die in a year? Some toxins discriminate with gender, yes they do. You can read about it here.

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