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All answers having "Contaminate" as clue:

4 Character Answers:

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SOIL

TOAD



5 Character Answers:

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EPSOM

LARGE

MAYBE

TAINT



6 Character Answers:

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DEBASE

DEFILE

INFECT

POISON



7 Character Answers:

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KETCHUP

POLLUTE



9 Character Answers:

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OTHERHALF

REFECTORY



10 Character Answers:

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ADULTERATE