Question: when was it discovered that lead was poisonous
[{'answer': 'at least 2000 BC', 'provenance': [{'wikipedia_id': '294338', 'title': 'Lead poisoning', 'start_paragraph_id': 4, 'start_character': 329, 'end_paragraph_id': 4, 'end_character': 345, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '294338', 'title': 'Lead poisoning', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 528, 'bleu_score': 0.8985154942681671, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17795815568815283387}, 'section': 'Section::::Abstract.'}]}]