3 ms·

I’m a little bit confused how plastic degrades so slowly that it lasts for thousands of years in the ocean and also loses particles fast enough to cause health

I’m a little bit confused how plastic degrades so slowly that it lasts for thousands of years in the ocean and also loses particles fast enough to cause health problems for those who drink or eat from it. How can it do both at once? Can someone who has seen the math clue me in? Feels like a logical contradiction.

barfbagginus 2y ago
Think of it as a half life. Suppose every piece of macro plastic sheds 0.1% of its mass yearly due to weathering, and suppose that there are 10 billion tons of plastic waste. We calculate 1. The half life 2. The microplastic production rate --------- import math # Define the rate at which macroplastic turns into microplastic per year rate_per_year = 0.1 / 100 # 0.1% # Half-life formula for exponential decay: T_half = ln(2 )/ decay_constant # Here, decay_constant is the rate_per_year half_life = math.log(2 ) / rate_per_year half_life # 693.1471805599452 years # Initial amount of macroplastic in metric tons initial_macroplastic = 10 * 10*9 # 10 billion metric tons # Annual production of microplastic is 0.1% of the initial macroplastic per year annual_microplastic = initial_macroplastic * rate_per_year annual_microplastic # 10 million metric tons. ------------- We produce 350 million tons of plastic waste a year. Over 30 years that's 10 billion tons. The .1% weathering rate was conservative. So weathering likely creates more than 10 million tons in microplastic annually. And will probably do so for at least a couple hundreds of years.
bestouff 2y ago
Like for many decays (e.g. nuclear) it starts to decay a lot at first, then it eases with time.
- deleted 2y ago
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hulitu 2y ago
It depends on the point that you're trying to make. Just like with burning of wood.
euroderf 2y ago
Relatively (structurally) weak in aggregate, relatively durable in bits ?
- pfannkuchen 2y ago
  I don’t think so because in the health risk case it must be very tiny bits falling off that gets you. People aren’t swallowing pieces of water bottle, it poisons you slowly over time (carcinogens). It could be that the shell has tiny bits that fall off easily when exposed to water but the inside is durable, but AFAIK it is a homogenous material.

barfbagginus 2y ago

Think of it as a half life. Suppose every piece of macro plastic sheds 0.1% of its mass yearly due to weathering, and suppose that there are 10 billion tons of plastic waste. We calculate 1. The half life 2. The microplastic production rate --------- import math # Define the rate at which macroplastic turns into microplastic per year rate_per_year = 0.1 / 100 # 0.1% # Half-life formula for exponential decay: T_half = ln(2 )/ decay_constant # Here, decay_constant is the rate_per_year half_life = math.log(2 ) / rate_per_year half_life # 693.1471805599452 years # Initial amount of macroplastic in metric tons initial_macroplastic = 10 * 10*9 # 10 billion metric tons # Annual production of microplastic is 0.1% of the initial macroplastic per year annual_microplastic = initial_macroplastic * rate_per_year annual_microplastic # 10 million metric tons. ------------- We produce 350 million tons of plastic waste a year. Over 30 years that's 10 billion tons. The .1% weathering rate was conservative. So weathering likely creates more than 10 million tons in microplastic annually. And will probably do so for at least a couple hundreds of years.

bestouff 2y ago

Like for many decays (e.g. nuclear) it starts to decay a lot at first, then it eases with time.

deleted 2y ago
[deleted]

hulitu 2y ago

It depends on the point that you're trying to make. Just like with burning of wood.

euroderf 2y ago

Relatively (structurally) weak in aggregate, relatively durable in bits ?

pfannkuchen 2y ago
I don’t think so because in the health risk case it must be very tiny bits falling off that gets you. People aren’t swallowing pieces of water bottle, it poisons you slowly over time (carcinogens). It could be that the shell has tiny bits that fall off easily when exposed to water but the inside is durable, but AFAIK it is a homogenous material.