You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Occupational exposure to pentachlorophenol causing lymphoma and hematopoietic malignancy for two generations. OBJECTIVE: Pentachlorophenol (PCP) is characterized as likely carcinogen of lymphoma and hematopoietic neoplasm. But the carcinogenicity to human was uncertain based on population studies. A systematic review was conducted to explore two kinds of associations, one was between the workers exposed to PCP with lymphoma and hematopoietic neoplasm, the other was between childhood lymphoma and leukemia with their parents exposed to PCP. METHODS: Systematic search for epidemiologic studies was carried out and the data were collected from MEDLINE database and from the reference lists of relevant studies. Data were extracted from 20 included studies published between 1986 and 2012. RESULTS: The meta-analysis suggested a significant association between lymphoma and workers' occupational exposing to PCP, for the pooled odds ratio = 2.57 (95% confidence interval (CI) = 1.52-4.35). The subgroup analysis indicated significant association for non-Hodgkin's lymphoma, but not for Hodgkin's disease. The cohort studies also showed comparatively higher relative risk (RR) and standardized mortality ratio (SMR). Two of the cohort studies found increased RR as the cumulative exposure time added. Another cohort study discovered that the white males had significantly elevated non-Hodgkin's lymphoma mortality (SMR = 1.98, 95% CI = 1.15-3.17), and males of other races had increased leukemia mortality (SMR = 4.57, 95% CI = 1.25-11.7). For the relationship of childhood leukemia and parental exposure to PCP, three published studies suggested an increased risk of childhood leukemia because of their parental exposure to PCP at the preconception period. CONCLUSION: Our review provided the evidence that occupational exposure of workers to PCP might increase the risk of lymphoma and hematopoietic neoplasm in themselves and in their children.
{"Chemical": ["PCP", "Pentachlorophenol", "pentachlorophenol"]}