This week, the ratings of four chemicals stocks on Portfolio Grader are down. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Marrone Bio Innovations, Inc. (MBII) earns an F (“strong sell”) this week, moving down from last week’s grade of D (“sell”). In Portfolio Grader’s specific subcategories of Earnings Momentum, Equity, Cash Flow and Sales Growth, MBII also gets F’s. For more information, get Portfolio Grader’s complete analysis of MBII stock.

This week, Innospec (IOSP) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Innospec manufactures fuel specialties, performance chemicals, and octane additives. Trade volume is up 428.4% from the previous week. To get an in-depth look at IOSP, get Portfolio Grader’s complete analysis of IOSP stock.

Celanese Corporation Class A (CE) is having a tough week. The company’s rating falls from a C to a D. Celanese is a global integrated producer of chemicals and advanced materials. The stock receives F’s in Earnings Growth, Earnings Momentum, Margin Growth and Sales Growth. For more information, get Portfolio Grader’s complete analysis of CE stock.

Dow Chemical Company’s (DOW) rating weakens this week, dropping to a D versus last week’s C. Dow Chemical is involved with the manufacture and sale of specialized products and services, such as chemicals, plastic materials, and agricultural products, as well as property and casualty insurance and reinsurance business. The stock also gets an F in Earnings Revisions. To get an in-depth look at DOW, get Portfolio Grader’s complete analysis of DOW stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.