Close a pollutant pulse account

Trace a pollutant pulse and its fate accounts

Original batch pulse · separate observed water-quality record · Original hypothetical parent substance in a well-mixed 1000 L store. Four discrete operations add supplied parent mass, export an aliquot and replace it with equal clean water, then transform a fraction of remaining parent. Step duration is unspecified. Transformation tracks original-parent equivalent, not product mass or harmlessness. No dose, ecological effect or safety inference is calculated.

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Reset keeps your prediction, captures and practice history.

Where did the parent substance go?

Single 40 g pulse; Export only: 25% exchange. Predict the final parent mass and its destinations before comparing captures. This fictional, well-mixed water store starts with zero parent substance in 1000 L. The four steps have no specified physical duration. Inputs and fractions are supplied teaching assumptions, not measured chemical rates.

1. Add the supplied parent mass with negligible water volume.
2. Export 25% of the mixed water and its parent substance, then replace it with the same volume of parent-free water. The store returns to 1000 L.
3. Transform 0% of the parent remaining after exchange. Track the amount converted as original-parent equivalent.
4. Record remaining parent and both cumulative fate accounts before the next addition.

Exported parent leaves this boundary; its downstream fate is not calculated. Transformed-parent equivalent means grams of original parent converted. It is not product mass, destruction of matter, mineralization or proof of harmlessness. Co-reactants and products are not explicitly modeled. This hypothetical transformable parent must not be relabeled an element such as lead that ordinary chemistry cannot destroy.

Final parent-equivalent balance: 40 g supplied = 12.65625 g parent remaining + 27.34375 g parent exported + 0 g original-parent equivalent transformed. Residual: 0 g.

Final parent concentration is 12.65625 mg/L. Convert grams to milligrams, then divide by 1000 L. Mass in grams and concentration in mg/L happen to have the same numerical value only because this store holds 1000 L. They remain different quantities.

Across the four operations, 1000 L leaves and 1000 L replaces it; final volume remains 1000 L. This is ordered batch exchange, not continuous flow. The transformation account does not track products' subsequent export or reactions.

Equal parent histories can hide different fates

Compare the single pulse with export only and transformation only. Both end at 30, 22.5, 16.875 and 12.65625 g parent. In the export case, 27.34375 g parent moved outside the store. In the transformation case, 27.34375 g original-parent equivalent was converted. Identical parent concentration histories do not establish identical products, exposures or effects.

Compare the single pulse and repeated additions under the same fate profile. Each supplies 40 g total, but its timing differs. A higher final parent store is an accounting result, not a prediction of organism uptake, food-chain magnification or biological harm.

Unavailable outputs: biological effect, internal dose and product mass are not calculated. No safe/unsafe label follows from these accounts, including the zero-source control. There is no duration from which to calculate exposure-time integrals or half-life.

Check the sequential operations and a dilution transfer

For a 40 g pulse with both operations, export removes 10 g, leaving 30 g. Transformation converts 7.5 g of that remainder, leaving 22.5 g. The two operations account for 43.75% of the original parent, not 50%; the second percentage uses a different starting amount.

Separate paper case: 12 g in 600 L is 20 mg/L. Adding 600 L clean water without exporting any parent gives 10 mg/L in 1200 L, while parent mass remains 12 g. That is dilution, not transformation or destruction. This paper case changes volume and is not a selectable recipe in the fixed-volume lab.

Final parent 12.65625 g; concentration 12.65625 mg/L in 1000 L.

40 g supplied parent = 12.65625 g remaining + 27.34375 g exported + 0 g transformed-parent equivalent. Products and biological effects are not calculated.