Toxicity of Petroleum and PAHs Sources, Ecotoxicology and Assessment

Introduction Oil has been naturally released into the environment for millennia Man-made spill is different  highly concentrated in a relatively small area  and often refined Typically there are 10 oil-consuming bacteria/L of seawater  after a spill increases to 50 million bacteria/L Used motor oil is a huge problem CA alone “loses” 200,000 – 300,000 gallons of used motor oil each years “down the drain”? Used on dogs for mange?

What is oil? (Sometimes called ohl, awl, oi-ul) A.Chemistry 1. Chemically complex  difficult to predict potential toxic effects 2.Crude oil = thousands of different organic compounds (mostly hydrocarbons) 3.Major classes of HC a.Alkanes (e.g. ethane, propane, butane) b.Cyclohexanes (napthenes) c.Aromatics (e.g. benzene, toluene, napthalene) 4.Oil from different sources has different composition a.Can determine the “finger print” of an oil sample  use for forensic spill source matching

What is Oil? B.Refined Oil - essentially done by distillation sseparates different fractions at different boiling points 1.Low temperatures (low boiling point)  gasoline 2.Medium temperatures  naptha  used in petrochemical industry 3.High temperatures  diesel oil > bunker oil (ships, electrical power plants) > tar is left (use on roads, roofs)

Toxicity of Oil Generally, as increase refinement Decrease toxicity to animals Increase “ “ plants A.Direct biological effects 1. Directly toxic compounds in petroleum include a.Polycyclic aromatic hydrocarbons (PAHs) b.Polychlorinated biphenyls (PCBs) c.Metals (especially Pb) Note: b and c above are very persistent in the environment

Polycyclic Aromatic Hydrocarbons (PAHs) Most studied petroleum product Defined as two or more fused benzene rings Type/concentration determines biological effect

Ring structures of representative PAHs Mostly aromatic Highly volatile High acute toxicity Low carcinogenicity Low volatility High chronic toxicity High carcinogenicity

PAHs (continued) Sensitivity crustaceans > insects > mollusks > algae > fish (can metabolize) Humans  mostly toxic as carcinogens

Toxicity of Oil B. Direct Biological Effects 1.Microbes  stimulatory  creates BOD, COD 2.Algae  low sensitivity to oil but highly sensitive to 2° effects a.Increase in primary production from 1)Death, decomposition, nutrient release of sensitive species 2)N-fixing species for certain oils b.Nothing dying?  decrease in primary productivity 3.Higher plants  reduction in Ps rates a.Changes cell permeability of cell membranes b.Direct absorption of light required by chloroplasts (because oil is THICK and BLACK)

Toxicity of Oil C.Factors Determining Ecotoxicology of Oil 1.Dosage/duration of exposure Size of spill, time to dispersal  lakes worse than rivers/streams 2.Type of oil (level of aromatics) Refined more toxic but evaporates/breaks down faster 3.Geographic location Oil breaks down more slowly in arctic than tropics 4.Season of year Weather, adult vs. juvenile (more sensitive) 5.Effects of oil on competing biota Competitive release 6.Ecosystem’s previous exposure to oil/other pollutants  tolerant organisms left (PICT)

Magnitude of problem Leaking Underground Storage Tanks (LUST 25% of all underground tanks > 15 years old are leaking (EPA estimate) 11 million gallons of gasoline seeps into ground annually (EPA estimate) Note: 1 gallon gasoline can pollute 1,000,000 gal of drinking water (undrinkable) Gas station in Thayer, MO was losing 100 gal./week (AR PC&E)  entering Spring River?

Magnitude Accidental spills Big name spills relatively minor Trains, planes, automobiles Refineries, drilling platforms (Mexican Ixtoc is worst spill in history) Boats Outboards very inefficient  discharge up to 1/3 of fuel into water

Summary Big problem even with lots of laws to prevent problem Why  we use so much of it! Next lecture  Exxon Valdez oil spill case history